Hydrocarbons: Class 11 Chemistry Chapter 9 Hinglish mein

Chemistry Part 2 · Hinglish notes, simulations aur practice · Official NCERT chapter PDF ↗

Published 22 Oct 2026 · Updated 22 Oct 2026

118 min
33 practice questions
41 MCQs

Is chapter mein aap kya seekhenge

Hydrocarbons ko classify karna aur alkanes, alkenes, alkynes aur arenes ke IUPAC naam dena, unke structural aur geometrical isomers samet
Samjhana ki alkanes, alkenes, alkynes aur benzene kaise banaye jaate hain, aur kisi diye gaye compound tak pahunchne ka route chunna
Alkane halogenation ka free-radical mechanism aur alkanes ke baaki reactions samjhana
Ethane ke Sawhorse aur Newman projections banana aur uske conformations ki stability compare karna
Alkenes aur alkynes par additions ke products predict karna, Markovnikov aur anti-Markovnikov orientation aur ozonolysis samet
Terminal alkynes ki acidity ko hybridisation ke zariye samjhana
Benzene ka structure aur stability samjhana, Hückel rule lagana, aur electrophilic substitution aur substituents ka directive influence samjhana
Hydrocarbons ko fuels aur raw materials ke roop mein pehchanna, aur benzene aur polynuclear hydrocarbons ki toxicity jaanna

NCERT Chemistry Class 11, Chapter 9, pp. 295–327 par based original companion text. Yeh NCERT se juda nahi hai aur NCERT ne ise endorse nahi kiya hai.

Ghar mein gas stove jalao, to tum ek hydrocarbon jala rahe ho. Zyaadatar Indian kitchens ke cylinder mein LPG (liquefied petroleum gas) hoti hai, jo mostly propane aur butane hai aur pressure mein liquid rakhi jaati hai. CNG autos aur buses compressed natural gas par chalti hain, jo mainly methane hai, aur LNG wahi gas hai jise lagbhag −162 °C tak thanda kiya jaata hai taaki tankers use oceans ke paar le ja sakein.

Hydrocarbon aisa compound hai jismein sirf carbon aur hydrogen hote hain. Lagbhag sabhi hydrocarbons zameen ke neeche ke teen stores se aate hain, crude oil, natural gas aur coal, aur thoda sa living sources se, jaise gaon ke gobar-gas plant ki biogas. Fuels hone ke alawa yeh chemical industry ka raw material bhi hain: paani ki bottle ka plastic, sports jersey ka synthetic fibre, painter ka thinner aur kai medicines, sabka source ek hydrocarbon tak jaata hai.

Is chapter mein hum chaar families padhenge — alkanes, alkenes, alkynes aur aromatic hydrocarbons. Har family ke compounds ka naam dena, unhe banana, aur unke reactions predict karna seekhoge, aur iske liye reaction mechanism hamara main tool hoga.

9.1 Classification

Chemists hydrocarbons ko do features se sort karte hain: kis tarah ke carbon–carbon bonds maujood hain, aur carbon skeleton open chain hai ya ring (Fig. 9.1). Saturated family mein sirf single bonds hote hain; ismein open-chain alkanes aur ring jaise cycloalkanes aate hain. Unsaturated compounds mein kam se kam ek multiple bond hota hai, aur aromatic compounds rings ka ek khaas group hain jiska typical example benzene hai.

3/3Benzene jaisi rings jinke ring electrons barabar share hote hain.

Fig. 9.1Teen families, bond type aur chain ya ring ke hisaab se sorted.NCERT p. 296

Ek tree diagram jiske top par Hydrocarbons hai aur teen branches hain. Step 1 saturated branch dikhata hai: open-chain alkanes jaise propane, C3H8, aur ring wale cycloalkanes jaise cyclohexane, C6H12. Step 2 unsaturated branch jodta hai: C=C bond wale alkenes, jaise ethene C2H4, aur C≡C bond wale alkynes, jaise ethyne C2H2. Step 3 aromatic branch jodta hai: arenes jaise benzene, C6H6, jise circle wale hexagon se dikhaya gaya hai.

Model banao

Hydrocarbon models banao

Tumhe chahiye

goondha hua atta ya clay, do size ki goliyon mein
jali hui matchsticks ya jhaadu ki seenk ke chhote tukde
do pipe cleaners

Pehle guess karo

Sirf single bonds se jude chaar carbons se, bina kisi ring ke, kitne alag skeletons bana sakte ho?

1234

Carbon atoms ke liye badi goliyan aur hydrogen atoms ke liye chhoti goliyan banao.
Har carbon mein chaar seenk lagao jo ek doosre se jitna ho sake door point karein, aur har hydrogen mein ek seenk. Methane banao.
Ek H nikaalo aur uski jagah apne hydrogens ke saath ek naya C lagao. Yahi repeat karke chaar carbons wale, bina ring ke, jitne skeletons ban sakein sab banao.
Do carbons ko ek seenk ki jagah do mudne wali strips se jodo. Ek carbon ko pakad kar doosre ko ghumane ki koshish karo.

Quick check

2 mein se 1

Inmein se kaun sa saturated hydrocarbon hai?

Ethene,

C_{2} H_{4}

Propyne,

C_{3} H_{4}

Benzene,

C_{6} H_{6}

Cyclohexane,

C_{6} H_{12}

Answer dekho

Answer (D) Cyclohexane, $C_{6} H_{12}$

Cyclohexane mein sirf single bonds hain, isliye woh saturated hai, bhale hi uska formula alkene ki tarah

C_{n} H_{2 n}

mein fit hota hai. Ring bhi do hydrogens utne hi kam karti hai jitna ek double bond.

9.2 Alkanes

Methane, $C H_{4}$ , sabse simple alkane hai: yeh marshes aur dhaan ke kheton se bubbles ban kar nikalti hai, coal mines mein jama hoti hai, aur biogas aur CNG ka zyaadatar hissa yahi hai. Ek $C H_{2}$ unit jodo to ethane, $C_{2} H_{6}$ , milta hai; ek aur jodo to propane, $C_{3} H_{8}$ , phir butane, $C_{4} H_{10}$ , aur aage bhi aise hi. Jo members $C H_{2}$ se alag hote hain, woh ek general formula wali homologous series banate hain:

Alkanes

C_{n} H_{2 n + 2}

jahan

$n$: carbon atoms ki sankhya (1, 2, 3, …)

Definition

Alkane

Ek saturated open-chain hydrocarbon, $C_{n} H_{2 n + 2}$ , jismein sirf C–C aur C–H single bonds hote hain.

ExampleLPG mein butane, $C_{4} H_{10}$ .

Alkane ka har carbon $s p^{3}$ hybridised hota hai. Uske chaar bonds ek regular tetrahedron ke corners ki taraf, 109.5° ke angle par point karte hain, isliye methane ek tetrahedron hai jiske centre mein carbon hai. Do $s p^{3}$ orbitals ke head-on overlap se C–C σ bond (154 pm) banta hai, aur ek $s p^{3}$ orbital ke hydrogen 1s orbital se overlap se C–H σ bond (112 pm) banta hai. Aise tetrahedra ki chains space mein zigzag hoti hain.

Room temperature par alkanes acids, bases aur zyaadatar oxidising agents ko ignore karte hain. Isiliye inka purana naam paraffins tha, jo Latin words se bana hai jinka matlab hai “bahut kam affinity”.

9.2.1 Nomenclature aur Isomerism

Methane, ethane aur propane mein se har ek sirf ek hi tarah se ban sakta hai. Chaar carbons se aage, ek molecular formula kai skeletons ko describe kar sakta hai. $C_{4} H_{10}$ ya to seedhi chaar-carbon chain hai, butane (n-butane), ya teen-carbon chain jiske beech wale carbon par methyl branch hai, 2-methylpropane (isobutane). $C_{5} H_{12}$ ke teen skeletons hain: pentane, 2-methylbutane aur 2,2-dimethylpropane. Same formula lekin alag carbon chains wale compounds chain isomers kehlaate hain, jo structural isomer ka ek type hai. Kyunki inke shapes alag hain, isliye yeh alag temperatures par boil aur melt hote hain (Section 9.2.3).

Table 9.1Alkanes ke chain isomers ki sankhya tezi se badhti hai

Formula	Straight-chain isomer ka naam	Chain isomers ki sankhya
$C_{4} H_{10}$	butane	2
$C_{5} H_{12}$	pentane	3
$C_{6} H_{14}$	hexane	5
$C_{7} H_{16}$	heptane	9
$C_{8} H_{18}$	octane	18
$C_{9} H_{20}$	nonane	35
$C_{10} H_{22}$	decane	75

Kisi skeleton ko describe karne ke liye, har carbon ke carbon neighbours gino. Ek neighbour ho to woh primary (1°) hai: har chain end primary hota hai, aur methane ka akela carbon bhi. Do neighbours ho to secondary (2°), teen ho to tertiary (3°) aur chaar ho to quaternary (4°). 2,2,4-trimethylpentane mein, yaani woh “iso-octane” jo petrol ka octane number tay karta hai, tum paanch 1°, ek 2°, ek 3° aur ek 4° carbon dhoondh sakte ho.

Example 9.1NCERT Problem 9.1 · p. 297

Paanch-carbon chain wale heptane isomers

$C_{7} H_{16}$ ke nau chain isomers hain. Unhe banao aur naam do jinki sabse lambi chain mein theek paanch carbons hain.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Alkane se ek hydrogen hata do to alkyl group, $C_{n} H_{2 n + 1}^{-}$ , milta hai, jise aksar R– likhte hain. Methyl ( $C H_{3}^{-}$ ) aur ethyl ( $C_{2} H_{5}^{-}$ ) ka ek-ek hi form hai. Propyl ke do forms hain, kyunki hydrogen ya to end carbon se liya ja sakta hai (propyl) ya beech wale carbon se (isopropyl, propan-2-yl).

Example 9.2NCERT Problem 9.2 · p. 298

Butyl groups ke isomers

Kitne alag butyl groups, $C_{4} H_{9}^{-}$ , hote hain? Har ek ko banao aur uske free bond par Cl lagane se jo chloroalkane milta hai uska naam do.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Unit 8 ke IUPAC rules chaar moves mein simat jaate hain: sabse lambi chain dhoondo; use aise number karo ki substituents ko sabse kam locants milein; substituents ke naam do aur unhe alphabetical order mein likho; phir parts ko jodo, numbers ke beech commas aur numbers aur words ke beech hyphens lagakar. Table 9.2 mein mushkil wale rules kaam karte dikhte hain.

Table 9.2Alkane ka naam tay karne wale rules

Condensed structure	IUPAC naam	Kaun sa rule
$(C H_{3})_{2} C H C H_{2} C H (C H_{3}) C H_{2} C H_{3}$	2,4-dimethylhexane	locants {2,4}, {3,5} se behtar hain
$C H_{3} C H_{2} C H (C_{2} H_{5}) C H (C H_{3}) C H_{2} C H_{3}$	3-ethyl-4-methylhexane	locants barabar hon to alphabet mein pehle wale ko kam number milta hai
$(C H_{3})_{3} C C H_{2} C H (C_{2} H_{5}) C H_{2} C H_{3}$	4-ethyl-2,2-dimethylhexane	alphabetical order mein di-, tri- ko ignore kiya jaata hai
$C H_{3} C H_{2} C H (C_{2} H_{5}) C H [C (C H_{3})_{3}] C H_{2} C H_{2} C H_{3}$	4-tert-butyl-3-ethylheptane	tert- aur sec- ignore hote hain (tert-butyl b ke under aata hai); iso- ignore nahi hota
$C H_{3} (C H_{2})_{3} C H [C H (C H_{3}) C H (C H_{3})_{2}] (C H_{2})_{3} C H_{3}$	5-(1,2-dimethylpropyl)nonane	branched substituent ko uske apne attachment point se number karte hain aur brackets mein likhte hain

Example 9.3NCERT Problem 9.3 · p. 299

Branched alkanes ke naam

Har ek ka IUPAC naam do: (i) $(C H_{3})_{3} C C H (C H_{3}) C H_{2} C H_{3}$ , (ii) $C_{2} H_{5} C (C H_{3})_{2} C H (C H_{3}) C_{2} H_{5}$ , (iii) $(C_{2} H_{5})_{4} C$ .

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Ulta chalna, yaani naam se structure tak, wahi rules ulte order mein lagata hai: parent chain banao, use number karo, numbered carbons par substituents lagao, aur aakhir mein har carbon ko itne hydrogens do ki uske chaar bonds poore ho jaayein (Fig. 9.2).

4/4Har carbon ko chaar bonds tak hydrogens milte hain: $C_{10} H_{22}$ .

Fig. 9.2Naam se structure tak: chain, numbers, substituents, hydrogens.NCERT p. 300

Top par 4-ethyl-2,3-dimethylhexane naam likha hai. Step 1 bonds se jude chhe carbon symbols ki chain banata hai. Step 2 unhe left se 1 se 6 tak number karta hai. Step 3 carbons 2 aur 3 par ek-ek CH3 group aur carbon 4 par ek C2H5 group lagata hai. Step 4 hydrogens jodta hai taaki har carbon ke chaar bonds hon, jisse chain par CH3, CH, CH, CH, CH2, CH3 milte hain, aur formula C10H22 note karta hai.

Example 9.4NCERT Problem 9.4 · p. 300

Naam se structures

(i) 3-ethyl-2,4-dimethylpentane aur (ii) 5-ethyl-2,2-dimethyloctane ke condensed formulas banao.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Example 9.5NCERT Problem 9.5 · p. 300

Galat naam theek karna

Neeche ka har naam koi rule todta hai. Jo structure woh describe karta hai use banao, galti dhoondo aur naam theek karo: (i) 5-ethyl-2-methylhexane; (ii) 3,3,5-trimethylhexane.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Quick check

3 mein se 1

(C H_{3})_{2} C H C H (C_{2} H_{5}) C H_{3}

ka IUPAC naam kya hai?

2,3-dimethylpentane2-ethyl-3-methylbutane3,4-dimethylpentane2-isopropylbutane

Answer dekho

Answer (A) 2,3-dimethylpentane

Sabse lambi chain ethyl group se hokar jaati hai (paanch carbons), aur methyls C2 aur C3 par hain. Jis naam mein 2-ethyl ho, uska matlab hamesha hai ki koi lambi chain chhoot gayi.

9.2.2 Preparation

Zyaadatar alkanes seedhe petroleum aur natural gas se milte hain. Laboratory mein reactions ki teen families inhe banati hain.

Unsaturated hydrocarbons se

Vanaspati ghee banane ke liye vegetable oil mein se, baarik nickel ke upar, hydrogen guzaari jaati hai, taaki hydrogen oil ke C=C bonds par add ho jaaye. Yahi hydrogenation kisi bhi alkene ya alkyne ko alkane mein badal deta hai. Catalyst ki zaroorat isliye hai kyunki H–H ek strong bond hai: metal surfaces hydrogen ko adsorb karke use dheela kar dete hain. Palladium aur platinum room temperature par hi kaafi active hain, jabki nickel, jo sasta industrial option hai, ko zyada temperature aur pressure chahiye.

But-2-ene aur propyne se alkanes

\begin{aligned} C H_{3} C H = C H C H_{3} \\ + H_{2} \overset{P t, P d o r N i}{\to} \\ C H_{3} C H_{2} C H_{2} C H_{3} \\ C H_{3} C \equiv C H + 2 H_{2} \\ \overset{P t, P d o r N i}{\to} \\ C H_{3} C H_{2} C H_{3} \end{aligned}

Alkyl halides se

(i) Zinc aur dilute hydrochloric acid alkyl chloride, bromide ya iodide (fluoride nahi) ke halogen ko hydrogen se replace karte hain:

2-Chlorobutane se butane

\begin{aligned} C H_{3} C H_{2} C H C l C H_{3} \\ + H_{2} \overset{Z n, H^{+}}{\to} \\ C H_{3} C H_{2} C H_{2} C H_{3} \\ + H C l \end{aligned}

(ii) Wurtz reaction mein dry ether mein sodium metal do alkyl groups ko jodta hai: $2 R X + 2 N a \overset{}{\to} R - R + 2 N a X$ . Ether mein paani bilkul nahi hona chahiye, kyunki sodium paani se react karta hai. Product mein alkyl halide se double carbons hote hain, isliye yeh method even number of carbons wale alkanes ke liye theek hai.

1-Bromopropane se hexane

\begin{aligned} 2 C H_{3} C H_{2} C H_{2} B r \\ + 2 N a \overset{d r y e t h e r}{\to} \\ C H_{3} (C H_{2})_{4} C H_{3} \\ + 2 N a B r \end{aligned}

Carboxylic acids se

(i) Decarboxylation. Soda lime sodium hydroxide aur calcium oxide ka mixture hai. Ise sodium carboxylate, RCOONa, ke saath garam karne par yeh –COONa group ko sodium carbonate ke roop mein hata deta hai aur uski jagah H laga deta hai, isliye chain ek carbon chhoti ho jaati hai:

Sodium propanoate se ethane

\begin{aligned} C H_{3} C H_{2} C O O N a \\ + N a O H \to_{h e a t}^{C a O} \\ C H_{3} C H_{3} + N a_{2} C O_{3} \end{aligned}

Example 9.6NCERT Problem 9.6 · p. 301

Salt chunna

Tumhe 2-methylpropane chahiye aur tumhare paas soda lime hai. Iske saath kaun sa sodium carboxylate garam karoge? Equation do.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

(ii) Kolbe's electrolytic method. Sodium ya potassium carboxylate ke concentrated aqueous solution ka electrolysis kiya jaata hai. Anode par har carboxylate ion ek electron kho deta hai; jo radical banta hai woh $C O_{2}$ chhod deta hai, aur do alkyl radicals judkar alkane banate hain. Cathode par hydrogen gas aur alkali bante hain (Fig. 9.3).

Sodium propanoate se butane

\begin{aligned} 2 C H_{3} C H_{2} C O O N a \\ + 2 H_{2} O \\ \overset{e l e c t r o l y s i s}{\to} \\ C H_{3} C H_{2} C H_{2} C H_{3} \\ + 2 C O_{2} + H_{2} \\ + 2 N a O H \end{aligned}

3/4Radical $C O_{2}$ kho deta hai; do ethyl radicals judkar butane banate hain.

Fig. 9.3Anode par butane banta hai; cathode par hydrogen.NCERT p. 301

Ek electrolysis cell jiske left mein positive anode aur right mein negative cathode hai, propanoate aur sodium ions ke solution mein. Step 1 cell aur ions dikhata hai. Step 2 dikhata hai ki anode par propanoate ion ek electron khokar propanoyloxy radical ban jaata hai. Step 3 dikhata hai ki woh radical carbon dioxide aur ethyl radical mein toot jaata hai, aur do ethyl radicals judkar butane banate hain. Step 4 dikhata hai ki cathode par paani electrons lekar hydrogen gas aur hydroxide ions deta hai.

Kyunki har product molecule do radicals se banta hai, isliye Kolbe's method se methane nahi ban sakti: sabse chhota possible product, ethanoate se, ethane hai.

9.2.3 Properties

Physical properties

C–C bonds non-polar hote hain aur C–H bonds lagbhag non-polar, kyunki carbon aur hydrogen ki electronegativities milti-julti hain. Isliye alkane molecules ek doosre ko sirf weak van der Waals (dispersion) forces se attract karte hain. 298 K par butane tak ke alkanes ( $C_{1}$ – $C_{4}$ ) gases hain, $C_{5}$ se $C_{17}$ tak liquids hain, aur 18 ya zyada carbons wale waxy solids hain. Pure alkanes colourless aur odourless hote hain; LPG ki smell ek sulfur compound se aati hai jo jaan-boojhkar milaya jaata hai taaki leak ka pata chal jaaye.

Non-polar hone ki wajah se alkanes paani mein nahi ghulte lekin doosre non-polar liquids ke saath aasani se mix ho jaate hain: like dissolves like. Isiliye petroleum jelly, jo bade alkanes ka naram mixture hai, sirf paani se haathon se nahi chhootti, lekin coconut oil ki kuch boondein use turant hata deti hain.

Series mein aage badhne par boiling points lagaataar badhte hain, kyunki bade molecules ka surface zyada hota hai jis par dispersion forces kaam karti hain (Fig. 9.4). Isomers mein branching boiling point ko kam karti hai. Branched molecule zyada compact, lagbhag ball jaisa hota hai, isliye paas ke molecules kam area par chhoote hain aur unhe alag karna aasan hota hai. Hexane 342 K par boil hota hai, jabki uska sabse branched isomer, 2,2-dimethylbutane, lagbhag 323 K par boil hota hai.

2/2Same formula, $C_{6} H_{14}$ : jitna zyada branched, utna kam boiling point.

Fig. 9.4Lambi chains zyada temperature par boil hoti hain; zyada branching kam par.NCERT Table 9.2 · p. 302

Step 1 methane se octane tak straight-chain alkanes ke boiling points ka vertical bar chart hai, jo 112 K se 399 K tak badhte hain, aur 298 K room-temperature line marked hai jisse dikhta hai ki pehle chaar gases hain. Step 2 paanch C6H14 isomers ka horizontal bar chart hai jiska axis 300 K se shuru hota hai: hexane 342 K, 3-methylpentane 336 K, 2-methylpentane 333 K, 2,3-dimethylbutane 331 K aur 2,2-dimethylbutane 323 K, sabse branched sabse neeche.

Chemical properties

Alkanes acids, bases, oxidising agents aur reducing agents ko jhel lete hain, lekin sahi conditions mein yeh neeche diye reactions karte hain.

1. Substitution (halogenation). Ultraviolet light ya diffused sunlight mein, ya tez garam karne par, ek halogen alkane ke hydrogens ko ek ke baad ek replace karta hai. Methane aur kaafi chlorine ho to chaaron replace ho sakte hain:

Stepwise chlorination (har step HCl bhi deta hai)

\begin{aligned} C H_{4} \overset{C l_{2}, h ν}{\to} C H_{3} C l \\ \overset{C l_{2}, h ν}{\to} C H_{2} C l_{2} \\ \overset{C l_{2}, h ν}{\to} C H C l_{3} \\ \overset{C l_{2}, h ν}{\to} C C l_{4} \end{aligned}

Fluorine itna reactive hai ki reaction control se bahar ho jaata hai, jabki iodine mushkil se react karta hai aur jo HI banta hai woh change ko ulta kar deta hai, jab tak HI ko khatam karne ke liye $H I O_{3}$ ya $H N O_{3}$ jaisa oxidant maujood na ho. Isliye kaam ke halogens chlorine aur bromine hain, aur reactivity ka overall order $F_{2} > C l_{2} > B r_{2} > I_{2}$ hai. Kaun sa hydrogen replace hota hai, yeh bhi matter karta hai: tertiary sabse tez, phir secondary, phir primary (3° > 2° > 1°). Lower alkanes par nitration aur sulphonation kaam nahi karte.

Iodination ko HI hatane ke liye oxidant chahiye

\begin{aligned} C_{2} H_{6} + I_{2} \overset{}{⇌} \\ C_{2} H_{5} I + H I \\ 5 H I + H I O_{3} \overset{}{\to} \\ 3 I_{2} + 3 H_{2} O \end{aligned}

Example

Chlorination kitna selective hai?

298 K par ek chlorine atom secondary hydrogen ko primary hydrogen se lagbhag 3.8 guna tezi se hataata hai. Propane, $C H_{3} C H_{2} C H_{3}$ , ke monochlorination mein 2-chloropropane ki percentage estimate karo.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Mechanism. Halogenation ek free-radical chain reaction hai jiske teen stages hain (Fig. 9.5). Free radical aisa atom ya group hai jismein ek unpaired electron hota hai, jise dot se dikhate hain.

Initiation. Light ya heat maujood sabse weak bond, Cl–Cl, ko aise todti hai ki har atom ek electron rakh leta hai (homolysis): $C l_{2} \overset{}{\to} 2 C l^{∙}$ .
Propagation. (a) $C l^{∙} + C H_{4} \overset{}{\to} C H_{3}^{∙} + H C l$ . (b) $C H_{3}^{∙} + C l_{2} \overset{}{\to} C H_{3} C l + C l^{∙}$ . Step (b) wahi chlorine atom wapas bana deta hai jo step (a) ko chahiye, isliye ek photon se hazaaron product molecules ban sakte hain. $C H_{3} C l$ par aise hi steps se $C H_{2} C l_{2}$ banta hai, aur aage bhi.
Termination. Radicals milte hain aur jodi bana lete hain: $C l^{∙} + C l^{∙} \overset{}{\to} C l_{2}$ , $C H_{3}^{∙} + C H_{3}^{∙} \overset{}{\to} C_{2} H_{6}$ aur $C H_{3}^{∙} + C l^{∙} \overset{}{\to} C H_{3} C l$ . Jab radicals ya reactants khatam ho jaate hain to chain ruk jaati hai.

Doosra termination step samjhata hai ki methane ke chlorination ke products mein hamesha thoda ethane kyun milta hai.

4/4Do radicals judte hain; ethane ek pehchaan wala by-product hai.

Fig. 9.5Ek photon chain shuru karta hai; radicals ki jodi use khatam karti hai.NCERT p. 303

Step 1, initiation: ek Cl–Cl molecule light absorb karke do chlorine atoms mein toot jaata hai, har ek par uske unpaired electron ka dot hai. Step 2, propagation (a): ek chlorine atom methane se hydrogen le leta hai, jisse HCl aur methyl radical bante hain. Step 3, propagation (b): methyl radical Cl2 se chlorine atom le leta hai, jisse chloromethane aur ek naya chlorine atom banta hai, aur ek curved arrow wapas step (a) tak jaakar chain dikhata hai. Step 4, termination: do radicals ke judne ke teen tarike, jinse Cl2, ethane ya chloromethane banta hai.

2. Combustion. Kaafi hawa ho to alkanes poori tarah jalkar carbon dioxide aur paani banate hain aur bahut zyada heat chhodte hain; ek mole methane 890 kJ deta hai. Kisi bhi alkane ke liye:

Alkane ka complete combustion

\begin{aligned} C_{n} H_{2 n + 2} + \frac{3 n + 1}{2} O_{2} \\ ⟶ n C O_{2} \\ + (n + 1) H_{2} O \end{aligned}

(9.19)

Hawa bahut kam ho to combustion incomplete hota hai: iski jagah zehreeli carbon monoxide aur kaalikh (carbon black) banti hai, jaise $C H_{4} + O_{2} \overset{}{\to} C + 2 H_{2} O$ . Carbon black printer ink, kaale pigments mein aur rubber tyres mein filler ke roop mein use hota hai.

Example

Kitchen cylinder mein energy

Ghar ke LPG cylinder mein 14.2 kg gas hoti hai. Ise pure butane maano ( $M = 58.1 g m o l^{- 1}$ , $Δ_{c} H = - 2878 k J m o l^{- 1}$ ). Poora cylinder kitni heat deta hai, aur kitne moles $O_{2}$ use karta hai?

Pehle khud try karo. Phir solution ek-ek step karke kholo.

3. Controlled oxidation. Oxygen ki niyantrit supply, catalyst aur sahi temperature aur pressure ho to oxidation beech mein ruk jaata hai aur kaam ke products deta hai:

523 K aur 100 atm par copper ke upar methane aur oxygen se methanol, $C H_{3} O H$ , banta hai;
garam $M o_{2} O_{3}$ ke upar methane aur oxygen se methanal, $H C H O$ , banta hai;
manganese(II) ethanoate ke saath ethane aur oxygen se ethanoic acid, $C H_{3} C O O H$ , banta hai;
tertiary hydrogen wala alkane, jaise 2-methylbutane, $K M n O_{4}$ se oxidise hokar tertiary alcohol banata hai, yahan 2-methylbutan-2-ol. Baaki alkanes par $K M n O_{4}$ ka asar nahi hota.

4. Isomerisation. Anhydrous $A l C l_{3}$ aur HCl gas ke saath garam karne par straight chain re-arrange hokar branched isomers ban jaati hai. Refineries ise use karti hain kyunki branched alkanes petrol engines mein zyada smoothly jalte hain.

Butane se 2-methylpropane

\begin{aligned} C H_{3} C H_{2} C H_{2} C H_{3} \\ \to_{H C l, h e a t}^{a n h y d \cdot A l C l_{3}} \\ (C H_{3})_{2} C H C H_{3} \end{aligned}

5. Aromatization (reforming). Refineries chhe ya zyada carbons wale straight-chain alkanes ki vapour ko alumina par lage vanadium, molybdenum ya chromium ke oxides ke upar se, lagbhag 773 K aur 10–20 atm par guzaarti hain. Chains hydrogen kho kar rings mein band ho jaati hain: hexane benzene ban jaata hai aur heptane toluene (methylbenzene).

Heptane se toluene

\begin{aligned} C H_{3} (C H_{2})_{5} C H_{3} \\ \to_{o x i d e c a t a l y s t}^{773 K, 10 - 20 a t m} \\ C_{6} H_{5} C H_{3} + 4 H_{2} \end{aligned}

6. Steam ke saath reaction. 1273 K par nickel ke upar methane aur steam se carbon monoxide aur hydrogen bante hain. Yeh hydrogen ka main industrial source hai, jaise fertiliser plants mein ammonia ke liye.

Steam reforming

\begin{aligned} C H_{4} + H_{2} O \\ \to_{1273 K}^{N i} C O + 3 H_{2} \end{aligned}

7. Pyrolysis (cracking). Hawa ke bina tez garam karne par, aksar catalyst ke upar, bade alkanes chhote alkanes aur alkenes mein toot jaate hain. Reaction free radicals se hota hai, aur chain kai jagah se toot sakti hai, isliye mixture banta hai. Cracking heavy oil fractions ko petrol aur fuel gas mein badal deta hai.

Decane ke kai possible tootne ke tariko mein se ek

\begin{aligned} C_{10} H_{22} \overset{h e a t}{\to} \\ C_{8} H_{18} + C_{2} H_{4} \end{aligned}

Quick check

4 mein se 1

Methane chlorination ka kaun sa by-product dikhata hai ki methyl radicals bante hain?

ethanehydrogenmethanolethene

Answer dekho

Answer (A) ethane

Ethane tabhi banta hai jab termination step mein do methyl radicals milte hain. Hydrogen nahi banti, kyunki chlorine atoms hydrogen ko HCl ke roop mein le jaate hain.

9.2.4 Conformations

Ethane ke ball-and-stick model ko ek carbon se pakdo aur doosre ko ghumao: woh aasani se ghoomta hai. Koi rukawat nahi aati, kyunki σ bond ka electron cloud C–C axis ke chaaron taraf cylinder jaisa hota hai, aur ek end ko ghumane se overlap nahi badalta. Molecule jin-jin arrangements se guzarta hai, unmein se har ek conformation hai (ise conformer ya rotamer bhi kehte hain): space mein aisa arrangement jo single bond ke around rotation se doosre mein badal jaata hai. Aise anginat conformations hote hain.

Definition

Conformations

Molecule ke aise spatial arrangements jo single bond ke around rotation se, bina koi bond tode, ek doosre mein badal jaate hain.

ExampleEclipsed aur staggered ethane.

Sach kahein to yeh ghoomna bilkul bina mehnat ke nahi hota. Jab paas wale carbons ke C–H bonds ek doosre ke paas se guzarte hain, to unke electron clouds ek doosre ko door dhakelte hain. Yeh torsional strain ek chhota energy barrier banata hai, alag molecules mein 1 se 20 kJ mol⁻¹ ke beech.

Ethane ke conformations

Ethane ke saare arrangements mein se do khaas hain. Eclipsed form mein front carbon ka har C–H bond back carbon ke ek bond ko chhupa leta hai, isliye hydrogens jitna ho sake utne paas hote hain. Staggered form mein front ka har C–H bond back ke do bonds ke theek beech mein point karta hai, jitna ho sake utna door. In dono ke beech ka koi bhi form skew form hai. Bond lengths aur angles poore time same rehte hain; sirf twist ka angle badalta hai.

Chemists do tarah ki drawings use karte hain (Fig. 9.6). Sawhorse projection C–C bond ko tirchhi nazar se dikhti ek lambi line ki tarah dikhata hai, front carbon neeche wale end par aur back carbon upar wale end par, har ek ke teen bonds 120° ke angle par. Newman projection C–C axis ke seedhe saath dekhta hai: front carbon woh point hai jahan teen bonds milte hain, aur back carbon ek circle hai jiske edge se teen chhote bonds nikalte hain.

3/3Back C–H bonds front wale bonds ke beech mein: dihedral angle 60°.

Fig. 9.6Back carbon ko 60° ghumane se eclipsed ethane staggered ethane ban jaata hai.NCERT Figs. 9.2, 9.3 · p. 305

Ethane ki do drawings saath-saath: left mein Sawhorse projection aur right mein Newman projection. Step 1 eclipsed form dikhata hai, jismein back hydrogens front wale ke theek peeche hain (thoda hatakar banaye gaye hain taaki dikh sakein). Step 2 ek curved arrow dikhata hai: back carbon 60 degrees ghoomta hai jabki front carbon ruka rehta hai. Step 3 staggered form dikhata hai, jismein har back hydrogen do front hydrogens ke beech mein hai aur dihedral angle 60 degrees label kiya gaya hai.

Axis ke saath dekhne par front C–H bond aur sabse paas wale back C–H bond ke beech ka angle dihedral (torsional) angle hai: eclipsed ethane ke liye 0°, staggered ke liye 60°. Torsional strain 0° par sabse zyada aur 60° par sabse kam hota hai, isliye staggered form ki energy sabse kam hai aur woh sabse stable hai. Fark chhota hai, lagbhag 12.5 kJ mol⁻¹, aur room temperature par aam collisions itni energy aasani se de dete hain. Isliye har ethane molecule ek second mein arabon baar forms badalta hai aur conformers kabhi alag nahi kiye ja sakte, haalaanki kisi bhi pal zyaadatar molecules staggered form ke paas hote hain. Isiliye C–C ke around rotation ko lagbhag free kehte hain, poori tarah free nahi.

InteractiveEthane conformations ka explorer

Ethane ka Newman projection: teen hydrogens ke saath front carbon aur teen hydrogens ke saath circle jaisa back carbon. Ek slider dihedral angle ko 0 se 360 degrees tak set karta hai, aur Play button back carbon ko dheere-dheere ghumata hai. Neeche ek graph torsional energy plot karta hai, jo 0, 120 aur 240 degrees par sabse zyada (12.5 kJ per mol) aur 60, 180 aur 300 degrees par zero hai, aur current angle par ek marker hai. Readouts angle, energy aur form ka naam dete hain: eclipsed, staggered ya skew.

Fig. 9.7Back carbon ko ghumane ke liye slider drag karo (ya Play dabao) aur energy ka badalna dekho.

9.3 Alkenes

Alkenes mein kam se kam ek carbon–carbon double bond hota hai. Har double bond alkane ke comparison mein do hydrogens kam kar deta hai, isliye ek C=C wale alkenes ka general formula $C_{n} H_{2 n}$ hai. Pehla stable member ethene, $C_{2} H_{4}$ (common naam ethylene) hai; $C H_{2}$ khud sirf ek pal ke liye exist karta hai. Purana naam olefins, yaani “oil banane wale”, yaad dilata hai ki ethene aur chlorine se ek oily liquid, 1,2-dichloroethane, banta hai.

Definition

Alkene

Kam se kam ek C=C double bond wala unsaturated hydrocarbon; ek double bond aur bina ring ke, $C_{n} H_{2 n}$ .

ExamplePropene, $C H_{3} C H = C H_{2}$ .

9.3.1 Double Bond ka Structure

C=C bond ka har carbon $s p^{2}$ hybridised hota hai. Har carbon ke ek $s p^{2}$ orbital ke head-on overlap se ek strong σ bond (lagbhag 397 kJ mol⁻¹) banta hai. Har carbon par bacha unhybridised 2p orbital molecule ke plane se right angle par khada hota hai, aur dono sideways overlap karke π bond (lagbhag 284 kJ mol⁻¹) banate hain (Fig. 9.8). Sideways overlap head-on overlap jitna effective nahi hota, isliye π bond kamzor partner hai.

Dono milkar double bond ko single bond se zyada strong (ethene mein lagbhag 681 kJ mol⁻¹, jabki ethane ke C–C ke liye 348 kJ mol⁻¹) aur chhota (134 pm vs 154 pm) banate hain, lekin double strong nahi. Ethene ke saare chhe atoms ek plane mein hain, aur bond angles 120° ke kareeb hain.

π electrons us plane ke upar aur neeche rehte hain, dheele bandhe hue aur khule. Electrons dhoondhne wale reagents, jinhe electrophiles kehte hain, inpar aasani se attack karte hain. Ek weak π bond ke badle do naye σ bonds banne se energy nikalti hai, isliye alkenes double bond ke across reagents add karte hain aur alkanes se kahin zyada reactive hain.

Definition

Electrophile

Electron dhoondhne wali species, positively charged ya electron-deficient, jo high electron density wale regions par attack karti hai.

Example $H^{+}$ , $B r^{+}$ , $N O_{2}^{+}$ .

3/4p orbitals sideways overlap karte hain: electron cloud upar aur neeche.

Fig. 9.8Axis ke saath ek σ bond aur uske upar-neeche ek π cloud.NCERT Figs. 9.4, 9.5 · p. 306

Ethene ko uske do carbons aur chaar hydrogens ke saath ek horizontal plane mein dikhaya gaya hai. Step 1 sigma framework dikhata hai: sp2 orbitals se bana ek C–C aur chaar C–H sigma bonds, lagbhag 120 degrees ke angles ke saath. Step 2 har carbon par ek seedha khada p orbital jodta hai, ek lobe plane ke upar aur ek neeche. Step 3 dikhata hai ki do p orbitals sideways overlap karke pi cloud banate hain, ek sausage C–C axis ke upar aur ek neeche. Step 4 C=C ki length 134 pm aur planar shape label karta hai.

9.3.2 Nomenclature

Alkene ka naam dene ke liye woh sabse lambi chain chuno jismein double bond ho, use double bond ke paas wale end se number karo, aur -ane ko -ene se badlo, saath mein pehle doubly bonded carbon ka locant do. Isliye $C H_{2} = C H C H_{2} C H_{2} C H_{3}$ pent-1-ene hai, $C H_{3} C H = C H C H_{2} C H_{3}$ pent-2-ene hai aur $(C H_{3})_{2} C = C H_{2}$ 2-methylprop-1-ene hai. Do double bonds hon to ending -diene hoti hai: $C H_{2} = C H - C H = C H - C H_{3}$ penta-1,3-diene hai.

Example 9.7NCERT Problem 9.7 · p. 307

Alkenes ke naam

In alkenes ke IUPAC naam do: (i) $C H_{2} = C H C H (C H_{3}) C H_{2} C H_{3}$ , (ii) $C H_{3} C H = C H C H = C H C H_{3}$ , (iii) $(C H_{3})_{2} C = C (C H_{3}) C H_{2} C H_{3}$ , (iv) $C H_{3} C H = C H C H (C H_{3}) C H (C H_{3})_{2}$ .

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Example 9.8NCERT Problem 9.8 · p. 307

σ aur π bonds ginna

Example 9.7 ke har molecule mein kitne σ aur π bonds hain?

Pehle khud try karo. Phir solution ek-ek step karke kholo.

9.3.3 Isomerism

Alkenes mein do tarah ki isomerism ho sakti hai: structural aur geometrical.

Structural isomerism. Ethene aur propene mein se har ek sirf ek tarah se ban sakta hai, lekin bade alkenes ke do tarah ke isomers hote hain. Pent-1-ene aur pent-2-ene ka skeleton same hai aur fark sirf double bond ki position ka hai, isliye yeh position isomers hain. 2-Methylbut-1-ene ka skeleton branched hai, isliye yeh dono ka chain isomer hai.

Example 9.9NCERT Problem 9.9 · p. 308

Bina branch wale hexenes

Unbranched chain wale saare $C_{6} H_{12}$ alkenes ke structures aur naam likho. Yeh kis tarah ke isomers hain, aur inmein se kaun cis aur trans forms mein exist kar sakte hain?

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Geometrical isomerism

Maan lo double bond ke har carbon par do alag groups hain, jaise XYC=CXY type ke molecule mein. Tab dono X groups double bond ki ek hi side par saath baith sakte hain, ya ek-ek dono sides par (Fig. 9.9). Single bond ke around yeh arrangements rotation se ek doosre mein badal jaate. Double bond ke around rotation ka matlab hoga π bond todna, jiske liye room temperature par collisions se milne wali energy se kahin zyada energy chahiye. Isliye dono arrangements alag compounds hain, jinhe geometrical isomers ya cis–trans isomers kehte hain.

Definition

Geometrical (cis–trans) isomerism

Same structure lekin double bond ke around groups ke alag arrangement wale compounds ke beech isomerism, jo restricted rotation ki wajah se hoti hai.

Examplecis- aur trans-but-2-ene.

cis (Latin, “is taraf”) ka matlab hai ki milte-julte groups double bond ki ek hi side par hain; trans (“us paar”) ka matlab hai ki woh opposite sides par hain. Dono mein atoms same order mein jude hain, isliye structure same hai, lekin space mein unka arrangement alag hai, jo configuration ka fark hai. Aise stereoisomers alag compounds hain jinhe separate kiya ja sakta hai, aur inki polarity, boiling point, melting point aur solubility alag hoti hai (neeche ki table dekho).

3/3Same structure, alag arrangement: cis polar hai, trans nahi.

Fig. 9.9C=C ke around restricted rotation cis aur trans isomers ko alag compounds bana deta hai.NCERT p. 308

Step 1 ek circular arrow ke saath C–C single bond dikhata hai: ek end free ghoom sakta hai. Step 2 upar-neeche pi lobes ke saath C=C bond dikhata hai; circular arrow cross kiya gaya hai kyunki ghumane se pi bond toot jaayega. Step 3 cis-1,2-dichloroethene dikhata hai jismein dono chlorines ek hi side par hain aur net dipole arrow unki taraf point karta hai (1.9 D), aur uske paas trans-1,2-dichloroethene hai jismein chlorines opposite sides par hain aur bond dipoles cancel ho jaate hain (0 D).

Model banao

Handshake model

Tumhe chahiye

ek partner

Pehle guess karo

Dono jodi haath jude hon to kya tum ek jodi ko bina chhode ghuma sakte ho?

Haan, aasani seSirf ek haath chhod karHaan, lekin sirf aadha turn

Apne partner ka right hand apne right hand se pakdo, jaise handshake mein. Dono apni kalaiyan ghumao: jude haath doorknob ki tarah ghoomte hain.
Ab unka left hand bhi apne left hand se pakdo. Wahi turn try karo.
Dhyaan do ki tumhare partner ka kaun sa haath tumhare left mein hai. Kya bina chhode sides badal sakte ho?

Table 9.3cis- aur trans-1,2-dichloroethene, ClCH=CHCl

Property	cis	trans
Dipole moment / D	1.90	0
Boiling point / K	333	322
Melting point / K	192	224

Cis isomer polar hai: uske do C–Cl bond dipoles kuch had tak ek hi taraf point karte hain aur jud jaate hain. Trans isomer mein woh opposite directions mein point karte hain aur cancel ho jaate hain. Extra dipole–dipole attraction cis isomer ko zyada boiling point deta hai. Solid mein zyada symmetrical trans molecules behtar pack hote hain, isliye trans isomer aam taur par zyada temperature par melt hota hai. But-2-ene bhi isi pattern ko follow karta hai: cis form thoda polar hai, trans form non-polar.

Geometrical isomerism ke liye har doubly bonded carbon par do alag groups chahiye. Yeh XYC=CXY, XYC=CXZ aur XYC=CZW mein hoti hai, lekin tab nahi jab kisi bhi carbon par do same groups hon, jaise $C H_{2} = C H C l$ ya $(C H_{3})_{2} C = C H C H_{3}$ mein.

Example 9.10NCERT Problem 9.10 · p. 309

Cis aur trans forms banana

Har compound ke dono geometrical isomers sketch karo aur unhe cis ya trans label karo: (i) pent-2-ene, $C H_{3} C H = C H C H_{2} C H_{3}$ ; (ii) 1,2-diphenylethene, $C_{6} H_{5} C H = C H C_{6} H_{5}$ .

Pehle khud try karo. Phir solution ek-ek step karke kholo.

Example 9.11NCERT Problem 9.11 · p. 309

Kaun cis ya trans ho sakta hai?

Woh compounds chuno jo cis aur trans forms mein exist kar sakte hain: (i) $C H_{2} = C H C l$ (ii) $C H_{3} C H = C H C l$ (iii) $(C H_{3})_{2} C = C H C H_{3}$ (iv) $C H_{3} C H_{2} C H = C H C H_{2} C H_{3}$ (v) $C l_{2} C = C H C H_{3}$

Pehle khud try karo. Phir solution ek-ek step karke kholo.

9.3.4 Preparation

Alkynes se

Hydrogen alkyne par do stages mein add hoti hai, aur pehle stage ke baad rokne ke liye naapi hui hydrogen aur kamzor kiya hua catalyst chahiye. Lindlar's catalyst, yaani charcoal par palladium jise sulfur compounds ya quinoline se thoda poison kiya gaya ho, cis alkene deta hai, kyunki dono hydrogen atoms metal surface se ek hi side se aate hain. Liquid ammonia mein sodium iski jagah trans alkene deta hai.

Pent-2-yne se koi bhi isomer

\begin{aligned} C H_{3} C \equiv C C_{2} H_{5} \\ \overset{H_{2}, L i n d l a r}{\to} cis \\ \overset{N a, l i q \cdot N H_{3}}{\to} trans \end{aligned}

Ethyne aur propyne ke liye charcoal par palladium ke upar partial hydrogenation ethene aur propene par ruk jaata hai, jahan cis ya trans ka sawaal hi nahi uthta.

Alkyl halides se

Alcoholic potash (ethanol mein ghula KOH) ke saath alkyl halide paas wale carbons se H aur X kho deta hai. Halogen wale carbon ko α aur agle ko β kehte hain, isliye yeh reaction β-elimination hai; kyunki HX hatta hai, isliye ise dehydrohalogenation bhi kehte hain. Speed dono partners par depend karti hai: C–I sabse aasani se tootta hai aur C–Cl sabse mushkil se (iodide > bromide > chloride), aur tertiary halides sabse tez react karte hain, phir secondary, phir primary.

1-Bromopropane se propene

\begin{aligned} C H_{3} C H_{2} C H_{2} B r \\ + K O H \to_{h e a t}^{e t h a n o l} \\ C H_{3} C H = C H_{2} \\ + K B r + H_{2} O \end{aligned}

Vicinal dihalides se

Zinc dust vicinal dihalide (jiske halogens paas-paas ke carbons par hon; naam Latin ke 'padosi' wale shabd se) se dono halogens hata deta hai, aur $Z n X_{2}$ aur ek C=C bond banta hai. Yeh dehalogenation hai.

2,3-Dibromobutane se but-2-ene

\begin{aligned} C H_{3} C H B r C H B r C H_{3} \\ + Z n \overset{}{\to} \\ C H_{3} C H = C H C H_{3} \\ + Z n B r_{2} \end{aligned}

Alcohols se acidic dehydration dwara

Garam concentrated sulfuric acid alcohol, R–OH, se ek water molecule kheench leta hai: –OH group aur β-carbon ka ek hydrogen saath mein nikalte hain, isliye yeh acidic dehydration bhi ek β-elimination hai.

Propan-2-ol se propene

\begin{aligned} C H_{3} C H (O H) C H_{3} \\ \to_{h e a t}^{c o n c \cdot H_{2} S O_{4}} \\ C H_{3} C H = C H_{2} + H_{2} O \end{aligned}

Quick check

3 mein se 1

Kaun sa reagent but-2-yne ko trans-but-2-ene mein badalta hai?

Liquid

N H_{3}

mein NaLindlar's catalyst ke saath

H_{2}

Ni ke saath

H_{2}

, heatzinc dust

Answer dekho

Answer (A) Liquid $N H_{3}$ mein Na

Liquid ammonia mein sodium trans alkene deta hai. Lindlar's catalyst cis alkene deta hai, aur excess hydrogen ke saath nickel seedha butane tak le jaata hai.

9.3.5 Properties

Physical properties

Physically alkenes alkanes ke kareebi cousins hain; sirf unki isomerism aur thodi polarity unhe alag karti hai. Har extra $C H_{2}$ par boiling points lagbhag 20–30 K badhte hain, aur branching unhe kam karti hai, isliye ethene, propene aur butenes gases hain, $C_{5}$ se lagbhag $C_{18}$ tak ke alkenes liquids hain, aur bade wale solids hain. Sab colourless hain, aur sirf ethene ki halki, meethi si smell hoti hai. Paani inhe nahi ghol pata, lekin benzene aur petroleum ether ghol lete hain.

Chemical properties

Alkenes ki zyaadatar chemistry addition hai: doubly bonded carbons par do naye groups jud jaate hain aur π bond khatam ho jaata hai. Aam taur par process ek electrophile shuru karta hai; kabhi-kabhi free radical (jaise neeche HBr aur peroxide ke saath). Alkenes ko oxidise bhi kiya ja sakta hai ya ozone se kaata ja sakta hai, aur khaas conditions mein yeh free-radical substitution bhi karte hain.

1. Hydrogen ka addition. Baarik nickel, palladium ya platinum ke upar alkenes hydrogen add karke alkanes dete hain (Section 9.2.2).

2. Halogens ka addition. Carbon tetrachloride mein reddish-orange bromine ki kuch boondein alkene ke saath hilao to rang lagbhag turant gayab ho jaata hai: bromine C=C bond ke across add hokar colourless vicinal dibromide deta hai. Yeh unsaturation ka ek jaldi hone wala laboratory test hai. Chlorine bhi isi tarah add hoti hai, lekin aam conditions mein iodine add nahi hoti. Mechanism, yaani ring jaise halonium ion se hone wala electrophilic addition, Class 12 mein aayega.

Propene se 1,2-dibromopropane (orange rang fade hota hai)

\begin{aligned} C H_{3} C H = C H_{2} + B r_{2} \\ \overset{C C l_{4}}{\to} \\ C H_{3} C H B r C H_{2} B r \end{aligned}

3. Hydrogen halides ka addition. HCl, HBr aur HI alkenes par add hokar alkyl halides dete hain, reactivity HI > HBr > HCl, yaani usi order mein jismein H–X bond kamzor hota jaata hai. Symmetrical alkene sirf ek product deta hai:

Hex-3-ene se 3-chlorohexane

\begin{aligned} C_{2} H_{5} C H = C H C_{2} H_{5} \\ + H C l \overset{}{\to} \\ C_{2} H_{5} C H_{2} C H C l C_{2} H_{5} \end{aligned}

Propene jaisa unsymmetrical alkene ya to 1-bromopropane de sakta hai ya 2-bromopropane. 1869 mein Russian chemist Vladimir Markovnikov ne ek rule mein bataya ki asal mein kaun sa banta hai:

Definition

Markovnikov rule

Jab H–X kisi unsymmetrical alkene par add hota hai, to hydrogen us doubly bonded carbon par jaata hai jispar pehle se zyada hydrogens hain, aur X doosre carbon par.

ExamplePropene + HBr se mainly 2-bromopropane banta hai.

Mechanism is rule ko samjhata hai (Fig. 9.10). Pehle, HBr ka electrophile $H^{+}$ π electrons par attack karke ek carbon se jud jaata hai, aur doosre carbon par positive charge, yaani carbocation, chhod deta hai. Agar $H^{+}$ end wale $C H_{2}$ carbon se jude, to secondary carbocation $C H_{3} - C H^{+} - C H_{3}$ banta hai; agar beech wale carbon se jude, to primary carbocation $C H_{3} C H_{2} C H_{2}^{+}$ . Secondary carbocation zyada stable hai, kyunki do alkyl groups uska charge failane mein madad karte hain, isliye woh jaldi banta hai aur jeet jaata hai. Doosre step mein $B r^{-}$ positive carbon se judta hai, aur major product 2-bromopropane milta hai.

4/4 $B r^{∙}$ pehle end carbon par add hota hai: 1-bromopropane (anti-Markovnikov).

Fig. 9.10Pehle koi bhi species attack kare, product zyada stable intermediate tay karta hai.NCERT p. 311

Step 1 propene, CH3–CH=CH2, dikhata hai jiske double bond ki taraf HBr ka H+ aa raha hai. Step 2 do possible carbocations dikhata hai: secondary wala, CH3–CH+–CH3, zyada stable marked, aur primary wala, CH3CH2CH2+, kam stable marked aur faded. Step 3 dikhata hai ki bromide ion secondary carbocation se judkar 2-bromopropane deta hai, jo Markovnikov product hai. Step 4 peroxide route dikhata hai: ek bromine atom end carbon par add hokar secondary radical CH3–CH•–CH2Br deta hai, jo HBr se H lekar 1-bromopropane deta hai, jo anti-Markovnikov product hai.

Peroxide effect. 1933 mein University of Chicago ke Morris Kharasch aur Frank Mayo ne paaya ki jab benzoyl peroxide jaisa organic peroxide maujood ho, to HBr propene par “ulta” add hota hai aur mainly 1-bromopropane deta hai. Yeh peroxide (Kharasch) effect, ya anti-Markovnikov addition, sirf HBr ke saath dikhta hai, HCl ya HI ke saath nahi.

HBr ka anti-Markovnikov addition

\begin{aligned} C H_{3} C H = C H_{2} + H B r \\ \overset{(C_{6} H_{5} C O)_{2} O_{2}}{\to} \\ C H_{3} C H_{2} C H_{2} B r \end{aligned}

Peroxide reaction ko free-radical chain mein badal deta hai. Uska weak O–O bond toot kar do radicals banata hai, jo $C O_{2}$ kho kar phenyl radicals dete hain; phenyl radical HBr se H leta hai aur ek bromine atom free kar deta hai. Ab $H^{+}$ nahi, balki $B r^{∙}$ pehle attack karta hai. End wale $C H_{2}$ par add hone se secondary radical banta hai, jo doosri taraf se bane primary radical se zyada stable hai. Woh radical ek aur HBr se H leta hai, jisse 1-bromopropane aur chain aage badhane ke liye ek naya $B r^{∙}$ milta hai:

Peroxide effect ki radical chain

\begin{aligned} (C_{6} H_{5} C O O)_{2} \overset{}{\to} \\ 2 C_{6} H_{5}^{∙} + 2 C O_{2} \\ C_{6} H_{5}^{∙} + H B r \overset{}{\to} \\ C_{6} H_{6} + B r^{∙} \\ C H_{3} C H = C H_{2} \\ + B r^{∙} \overset{}{\to} \\ C H_{3} C^{∙} H C H_{2} B r \\ + H B r \overset{}{\to} \\ C H_{3} C H_{2} C H_{2} B r \\ + B r^{∙} \end{aligned}

Sirf HBr hi kyun? H–Cl bond (lagbhag 431 kJ mol⁻¹) carbon radical ke todne ke liye bahut strong hai, isliye chain aage nahi badh paati. H–I bond (lagbhag 299 kJ mol⁻¹) aasani se toot jaata hai, lekin iodine atoms double bond par add hone ki jagah judkar $I_{2}$ ban jaate hain. H–Br (lagbhag 366 kJ mol⁻¹) beech mein hai, aur dono chain steps aaraam se chalte hain.

Example 9.12NCERT Problem 9.12 · p. 312

HBr aur 2-methylpropene

2-Methylpropene, $(C H_{3})_{2} C = C H_{2}$ , ko HBr ke saath treat kiya jaata hai. Main product predict karo aur naam do (i) simple reaction ka aur (ii) benzoyl peroxide ki maujoodgi mein hue reaction ka.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

4. Sulfuric acid ka addition. Thande concentrated sulfuric acid mein alkene guzaarne par alkyl hydrogen sulfate banta hai, jismein $- O S O_{3} H$ us carbon par hota hai jo Markovnikov's rule predict karta hai:

Markovnikov orientation (but-1-ene mein R = C₂H₅: butan-2-yl hydrogen sulfate)

\begin{aligned} R C H = C H_{2} \\ + H_{2} S O_{4} \overset{}{\to} \\ R C H (O S O_{3} H) C H_{3} \end{aligned}

5. Paani ka addition. Akela paani kuch nahi karta, lekin concentrated sulfuric acid ki kuch boondein uske addition ko catalyse karti hain. H zyada hydrogens wale carbon par jaata hai aur –OH doosre par, jisse alcohol banta hai:

2-Methylpropene se 2-methylpropan-2-ol

\begin{aligned} (C H_{3})_{2} C = C H_{2} \\ + H_{2} O \overset{H^{+}}{\to} \\ (C H_{3})_{3} C O H \end{aligned}

6. Oxidation. (a) Baeyer's test. Purple, thanda, dilute alkaline permanganate (Baeyer's reagent) alkene ke saath hilane par apna rang kho deta hai, aur brown manganese dioxide dikhne lagta hai. Har doubly bonded carbon par ek –OH group add ho gaya hai, jisse vicinal diol (glycol) banta hai.

Propene se propane-1,2-diol

\begin{aligned} C H_{3} C H = C H_{2} \\ + H_{2} O + [O] \\ \overset{c o l d d i l \cdot K M n O_{4}}{\to} \\ C H_{3} C H (O H) C H_{2} O H \end{aligned}

(b) Garam acidic permanganate ya acidic dichromate aur aage jaakar double bond tod deta hai. Har doubly bonded carbon aakhir mein ek C=O group mein aata hai: do alkyl groups wala carbon ketone ban jaata hai, hydrogen wala carbon carboxylic acid ban jaata hai, aur terminal $= C H_{2}$ poori tarah carbon dioxide aur paani tak oxidise ho jaata hai.

2-Methylbut-2-ene se propanone aur ethanoic acid

\begin{aligned} (C H_{3})_{2} C = C H C H_{3} \\ \overset{K M n O_{4} / H^{+}}{\to} \\ (C H_{3})_{2} C = O \\ + C H_{3} C O O H \end{aligned}

7. Ozonolysis. Ozone double bond ke across add hokar ek unstable ozonide deta hai, jise phir zinc aur paani do carbonyl compounds mein tod dete hain (Fig. 9.11). Products predict karna aasan hai: C=C bond kaato aur har carbon par =O lagao. Ulta chalein to products bilkul batate hain ki double bond kahan tha, isiliye ozonolysis ko unknown compounds mein double bonds locate karne ke liye use kiya jaata hai.

Pent-2-ene se ethanal aur propanal

\begin{aligned} C H_{3} C H = C H C_{2} H_{5} \\ \to_{(i i) Z n / H_{2} O}^{(i) O_{3}} \\ C H_{3} C H O \\ + C_{2} H_{5} C H O \end{aligned}

4/4Ek carbon se propanone, doosre se ethanal.

Fig. 9.11C=C bond kaato aur har carbon par =O lagao.NCERT p. 313

Step 1 2-methylbut-2-ene, (CH3)2C=CH–CH3, dikhata hai jismein double bond highlighted hai. Step 2 dikhata hai ki ozone double bond ke across add hokar do carbons aur teen oxygens wali paanch-membered ozonide ring banata hai. Step 3 purane double bond ke beech se ek dashed cutting line aur label Zn aur H2O dikhata hai. Step 4 do products dikhata hai: left carbon se propanone, (CH3)2C=O, aur right carbon se ethanal, O=CH–CH3, dono mein ab wahan C=O group hai jahan double bond tha.

Example

Ozonolysis products ko decode karna

Ek alkene $C_{6} H_{12}$ ozonolysis par propanone aur propanal deta hai. Alkene pehchano.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

8. Polymerisation. Heat aur pressure mein, aur catalyst ke saath, ethene ke hazaaron molecules ek ke baad ek jud jaate hain. Yeh polymerisation hai: chhoti units monomers hain aur lambi chain wala product, yahan polythene, polymer hai. Propene bhi isi tarah polymerise hokar polypropene banata hai.

Polythene aur polypropene

\begin{aligned} n C H_{2} = C H_{2} \\ \to_{h e a t, p r e s s u r e}^{c a t a l y s t} \\ (- C H_{2} - C H_{2}^{-})_{n} \\ n C H_{3} C H = C H_{2} \\ \overset{c a t a l y s t}{\to} \\ (- C H (C H_{3}) - C H_{2}^{-})_{n} \end{aligned}

Polythene se carry bags, cling film, paani ki tankiyan aur cable insulation bante hain; polypropene se chairs, food containers, rassiyan aur non-woven shopping bags. Inki mazbooti hi inki kami bhi hai: phenka gaya plastic sadiyon tak rehta hai, aur yeh ek wajah hai ki India ne 2022 mein kai single-use plastic items ban kiye.

InteractiveAlkene reactions ki bench

Buttons ki do rows: chhe alkenes (ethene, propene, but-1-ene, but-2-ene, 2-methylpropene aur 2-methylbut-2-ene) aur aath reagents (nickel ke saath hydrogen, CCl4 mein bromine, HBr, peroxide ke saath HBr, acid ke saath paani, Baeyer's reagent, ozone phir zinc aur paani, aur garam acidic permanganate). Panel reaction ko reactant, reagent aur product formulas ke roop mein dikhata hai, products ke IUPAC naam, koi rang ka badlav, aur rule samjhane wali ek line, jaise Markovnikov orientation ya double bond kahan kata.

Fig. 9.12Product aur use tay karne wala rule dekhne ke liye ek alkene aur ek reagent chuno.

9.4 Alkynes

Alkynes mein kam se kam ek carbon–carbon triple bond hota hai. Utne hi carbons wale alkane se inmein chaar hydrogens kam hote hain, isliye ek triple bond ke liye general formula $C_{n} H_{2 n - 2}$ hai. Pehla member ethyne, $H C \equiv C H$ , hai, jise acetylene naam se zyada jaana jaata hai. Oxyacetylene torch mein pure oxygen ke saath jalane par yeh 3000 °C se zyada ki flame deta hai, jo steel ko kaatne aur weld karne ke liye kaafi garam hai. Alkynes kai tarah ke organic compounds ke starting materials bhi hain.

Definition

Alkyne

Kam se kam ek C≡C triple bond wala unsaturated hydrocarbon; ek triple bond aur bina ring ke, $C_{n} H_{2 n - 2}$ .

ExamplePropyne, $C H_{3} C \equiv C H$ .

9.4.1 Nomenclature aur Isomerism

Common names alkynes ko acetylene ke derivatives maante hain: $C H_{3} C \equiv C H$ methylacetylene hai aur $C H_{3} C \equiv C C H_{3}$ dimethylacetylene. IUPAC names mein -ane ki jagah -yne lagta hai aur pehle triply bonded carbon ka locant diya jaata hai, isliye yeh dono propyne aur but-2-yne hain, jabki $C H_{3} C H_{2} C \equiv C H$ but-1-yne hai. Ethyne aur propyne ka ek-ek hi structure hai. Chaar carbons ke saath triple bond C1 ya C2 se shuru ho sakta hai, isliye but-1-yne aur but-2-yne position isomers hain; paanch ya zyada carbons ke saath branched chain isomers bhi aa jaate hain.

Example 9.13NCERT Problem 9.13 · p. 315

C6H10 ke terminal alkynes

Un saare $C_{6} H_{10}$ alkynes ke structures aur naam likho jinka triple bond chain ke end par hai. Yeh aapas mein kaun si isomerism dikhate hain?

Pehle khud try karo. Phir solution ek-ek step karke kholo.

9.4.2 Triple Bond ka Structure

Ethyne ek seedha molecule hai, H–C≡C–H jismein angles 180° hain, kyunki har carbon $s p$ hybridised hai aur uske do $s p$ orbitals opposite directions mein point karte hain (Fig. 9.13). Inmein se ek apne partner ke saath head-on overlap karke C–C σ bond banata hai; doosra ek hydrogen se bond banata hai.

Isse har carbon ke paas do extra 2p orbitals bachte hain, jo ek doosre se aur molecular axis se right angle par hain. Dono carbons ke matching pairs sideways overlap karte hain, aur perpendicular planes mein do π bonds bante hain. Isliye ethyne mein teen σ bonds (ek C–C, do C–H) aur carbons ke beech do π bonds hain, aur dono π clouds mil kar C–C axis ke chaaron taraf barabar lipti electron density ki ek sleeve ban jaate hain.

Table 9.4Carbon–carbon bonds ka comparison

Bond	Example	Carbon ka hybridisation	s character	Length / pm	Bond enthalpy / kJ mol⁻¹
C–C	ethane	$s p^{3}$	25 %	154	348
C=C	ethene	$s p^{2}$	33 %	134	681
C≡C	ethyne	$s p$	50 %	120	823

3/3Sideways overlap se do π bonds bante hain: charge ka ek cylinder, C≡C 120 pm.

Fig. 9.13Ek σ bond aur do perpendicular π bonds se linear molecule banta hai.NCERT Fig. 9.6 · p. 315

Ethyne ko seedhi line H–C–C–H ki tarah dikhaya gaya hai. Step 1 sp orbitals se bane sigma bonds aur 180 degree ka angle dikhata hai. Step 2 har carbon par do p orbitals jodta hai: ek pair upar-neeche khada, aur ek pair ellipses ki tarah jo dekhne wale ki taraf aur usse door point karta hai. Step 3 dikhata hai ki yeh sideways overlap karke do pi bonds banate hain, jo C–C axis ke around electron density ke ek cylinder mein mil jaate hain, label 120 pm.

9.4.3 Preparation

1. Calcium carbide se. Industry ke liye ethyne limestone se shuru hota hai. Tez garam karne se quicklime milta hai; electric furnace mein quicklime aur coke ko fuse karne se calcium carbide milta hai; aur carbide mein paani daalne se ethyne milta hai:

Limestone se ethyne

\begin{aligned} C a C O_{3} \overset{h e a t}{\to} \\ C a O + C O_{2} \\ C a O + 3 C \overset{}{\to} \\ C a C_{2} + C O \\ C a C_{2} + 2 H_{2} O \overset{}{\to} \\ C a (O H)_{2} + C_{2} H_{2} \end{aligned}

Yahi reaction kabhi miners aur raat ke bazaaron ke sisakte carbide lamps ko jalata tha. Ek gair-kanooni practice ke peeche bhi yahi hai: kabhi-kabhi kachche aamon ke beech calcium carbide chhupa diya jaata hai, kyunki usse nikalne wala ethyne natural ripening gas, ethene, ki nakal karta hai.

2. Vicinal dihalides se. Lagaataar do eliminations vicinal dihalide ko alkyne mein badal dete hain. Alcoholic KOH pehla HX aasani se hata deta hai aur ek vinylic (alkenyl) halide bachta hai; doosre HX ke liye, jo doubly bonded carbon par hai, kahin zyada strong base sodamide, $N a N H_{2}$ , chahiye.

1,2-Dibromopropane se propyne

\begin{aligned} C H_{3} C H B r C H_{2} B r \\ \overset{a l c \cdot K O H}{\to} \\ C H_{3} C H = C H B r \\ \overset{N a N H_{2}}{\to} C H_{3} C \equiv C H \end{aligned}

9.4.4 Properties

Physical properties

Alkynes bhi pehle dekhe pattern mein fit hote hain: molar mass ke saath melting point, boiling point aur density badhte hain, isliye teen sabse chhote gases hain, agle aath liquids aur baaki solids. Yeh colourless, weakly polar, paani se halke aur usmein insoluble hain, lekin benzene, ether aur carbon tetrachloride mein ghul jaate hain. Pure ethyne mein lagbhag koi smell nahi hoti; carbide acetylene ki lahsun jaisi smell phosphine jaisi impurities se aati hai.

Chemical properties

A. Acidic character. Terminal alkyne bahut weak acid hai, phir bhi alkene ya alkane se kahin zyada strong. Ethyne sodium metal ya sodamide jaise strong bases ko proton de deta hai aur sodium ethynide banata hai; ethene aur ethane aisa koi reaction nahi dikhate. Hybridisation is fark ko samjhata hai. $s p$ orbital aadha s (50 %) hota hai, jabki $s p^{2}$ ek-tihai aur $s p^{3}$ ek-chauthai, aur s electrons nucleus ke paas rehte hain. Isliye $s p$ carbon teenon mein sabse zyada electronegative hai, C–H bonding pair uske zyada paas rehta hai, aur $H^{+}$ sabse aasani se nikalta hai.

Terminal alkynes sodium alkynides banate hain

\begin{aligned} 2 H C \equiv C H + 2 N a \overset{}{\to} \\ 2 H C \equiv C N a + H_{2} \\ C_{2} H_{5} C \equiv C H \\ + N a N H_{2} \overset{}{\to} \\ C_{2} H_{5} C \equiv C N a + N H_{3} \end{aligned}

Yeh acidity sirf ≡C–H hydrogen ki hai; propyne ke methyl hydrogens propane ke hydrogens se zyada acidic nahi hain. Isliye but-1-yne sodamide se react karta hai jabki but-2-yne, jismein ≡C–H nahi hai, nahi karta. Yeh terminal alkynes ko alkanes, alkenes aur internal alkynes se alag pehchanne ka aasan tarika hai. Acidity ke orders $H C \equiv C H > H_{2} C = C H_{2} > C H_{3} C H_{3}$ aur $H C \equiv C H > C H_{3} C \equiv C H$ ≫ $C H_{3} C \equiv C C H_{3}$ hain. Lagbhag pKa values: ethyne 25, ethene 44, ethane 50. Ethyne bhi paani (pKa lagbhag 16) se kahin zyada weak acid hai.

B. Addition reactions. Triple bond hydrogen, halogen ya hydrogen halide ke do molecules, ek ke baad ek, le sakta hai. Inmein se zyaadatar additions electrophilic hain. Unsymmetrical alkyne mein orientation Markovnikov's rule follow karti hai, jo pehle step mein bane vinylic cation (doubly bonded carbon par positive charge) ki stability se tay hoti hai.

(i) Hydrogen. Pt, Pd ya Ni ke upar pehle alkene banta hai aur jaldi hi aage hydrogenate hokar alkane ban jaata hai.

But-2-yne se butane

\begin{aligned} C H_{3} C \equiv C C H_{3} \\ \overset{H_{2}, N i}{\to} \\ [C H_{3} C H = C H C H_{3}] \\ \overset{H_{2}, N i}{\to} \\ C H_{3} C H_{2} C H_{2} C H_{3} \end{aligned}

(ii) Halogens. Bromine do baar add hokar tetrabromide deta hai, aur $C C l_{4}$ mein bromine ka reddish-orange rang fade ho jaata hai, jo alkenes jaisa hi unsaturation ka test hai.

Propyne se 1,1,2,2-tetrabromopropane

\begin{aligned} C H_{3} C \equiv C H + 2 B r_{2} \\ \overset{}{\to} C H_{3} C B r_{2} C H B r_{2} \end{aligned}

(iii) Hydrogen halides. HX ke do molecules add hote hain. Markovnikov's rule dono halogens ko ek hi carbon par bhejta hai, jisse geminal (gem) dihalide banta hai:

But-1-yne se 2,2-dibromobutane

\begin{aligned} C_{2} H_{5} C \equiv C H + H B r \\ \overset{}{\to} C_{2} H_{5} C B r = C H_{2} \\ \overset{H B r}{\to} C_{2} H_{5} C B r_{2} C H_{3} \end{aligned}

(iv) Paani. Akela paani alkynes ko nahi chhoota. Mercury(II) ions ko catalyst banakar, yaani lagbhag 333 K par dilute sulfuric acid mein mercury(II) sulfate ke saath, paani ka ek molecule add hota hai. Pehla product, ek enol (doubly bonded carbon par –OH), turant re-arrange hokar carbonyl compound ban jaata hai. Ethyne se ethanal milta hai; baaki har alkyne ketone deta hai.

Propyne se propanone

\begin{aligned} C H_{3} C \equiv C H + H_{2} O \\ \to_{333 K}^{H g^{2 +}, H_{2} S O_{4}} \\ [C H_{3} C (O H) = C H_{2}] \\ \overset{}{\to} C H_{3} C O C H_{3} \end{aligned}

(v) Polymerisation. (a) Linear. Sahi conditions mein ethyne judkar polyacetylene (polyethyne) banata hai, jo alternate double aur single bonds ki lambi chain hai, $(- C H = C H - C H = C H^{-})_{n}$ . Iski khaas treated films electricity conduct karti hain aur inhe batteries ke liye halke, saste electrodes ki tarah try kiya gaya hai.

(b) Cyclic. 873 K par laal-garam iron tube mein teen ethyne molecules band hokar ek benzene ring bana lete hain, jo open-chain (aliphatic) aur aromatic chemistry ke beech seedha link hai.

Ethyne se benzene

\begin{aligned} 3 H C \equiv C H \\ \to_{873 K}^{r e d - h o t F e} C_{6} H_{6} \end{aligned}

Example 9.14NCERT Problem 9.14 · p. 318

Limestone se benzene tak

Sirf limestone, coke aur paani (aur heat aur ek iron tube) use karke batao ki benzene kaise banaoge.

Pehle khud try karo. Phir solution ek-ek step karke kholo.

9.5 Aromatic Hydrocarbon

Toluene, naphthalene aur inke rishtedaar arenes, ya aromatic hydrocarbons, hain. Naam historical hai: kai shuruaati examples ki khushboo achhi thi (Greek aroma), lekin aaj yeh label structure batata hai, smell nahi. Zyaadatar arenes mein ek benzene ring hoti hai, jo zyaadatar reactions mein apni unsaturation bachaye rakhti hai; yeh benzenoid arenes hain, jaise toluene (methylbenzene), xylenes, naphthalene (do fused rings) aur biphenyl (do judi rings). Kuch aromatic species doosri tarah ki ring par bani hoti hain, jaise Section 9.5.3 mein cyclopentadienyl anion; yeh non-benzenoid hain.

Definition

Arene (aromatic hydrocarbon)

Ek ya zyada aromatic rings, aam taur par benzene rings, wala hydrocarbon.

ExampleToluene, naphthalene.

9.5.1 Nomenclature aur Isomerism

Benzene par ek substituent lagao to koi fark nahi padta ki kaun sa carbon chuna, kyunki chhe ke chhe equivalent hain: sirf ek chlorobenzene aur ek toluene hai. Doosra substituent bagal mein, ek carbon aur door, ya theek saamne ja sakta hai, jisse teen position isomers milte hain: ortho (o-, 1,2), meta (m-, 1,3) aur para (p-, 1,4). Doosri taraf se gine to 1,6 bhi ortho hai aur 1,5 bhi meta. Dichlorobenzenes aur xylenes (dimethylbenzenes) dono in teen forms mein aate hain; Unit 8 mein inke naam hain.

9.5.2 Benzene ka Structure

Benzene ka formula, $C_{6} H_{6}$ , Michael Faraday ke 1825 mein ise isolate karne ke kuch hi samay baad pata chal gaya tha, lekin iska structure tay hone mein chaar dashak lage. Har proposal ko teen ajeeb facts samjhane the. Formula bahut zyada unsaturation dikhata hai, phir bhi benzene asaadharan roop se stable hai aur alkenes jaise additions nahi karta. Yeh triozonide banata hai, jaise iske teen C=C bonds hon. Aur yeh sirf ek monosubstituted product deta hai, isliye chhe ke chhe C–H units ek jaise hone chahiye.

1865 mein August Kekulé ka jawab tha carbons ka ek hexagon jo alternate single aur double bonds se juda ho, aur har carbon par ek hydrogen ho. Dikkat yeh thi: aisi ring se do 1,2-dibromobenzenes milne chahiye, ek mein bromines double bond ke across aur ek mein single bond ke across, lekin sirf ek exist karta hai. Kekulé ne kaha ki double bonds itni tezi se jagah badalte rehte hain ki dono forms alag nahi kiye ja sakte. Yeh bhi nahi samjha paaya ki benzene itna stable kyun hai ya woh addition ki jagah substitution kyun pasand karta hai.

Benzene ki resonance aur stability

Aaj dono Kekulé structures ko aage-peeche palatne wale forms nahi, balki resonance structures maana jaata hai, jinmein se koi bhi akele exist nahi karta. Asli molecule, yaani resonance hybrid, in dono ke beech hai, aur uske chhe ke chhe ring bonds ek jaise hain. Chemists ise andar circle wale hexagon se dikhate hain (Fig. 9.14); circle un chhe π electrons ko dikhata hai jo teen double bonds mein band hone ki jagah poori ring par barabar faile hain.

Orbitals bhi yahi kehaani batate hain. Har ring carbon $s p^{2}$ hybridised hai, isliye chhe C–C aur chhe C–H bonds ka σ framework flat hai, 120° angles ke saath. Har carbon ek p orbital bhi rakhta hai jo ring se seedha khada hai. Agar yeh p orbitals jodi bana kar teen alag π bonds banate, to aisa karne ke do barabar achhe tarike hote: dono Kekulé structures. Iski jagah har p orbital apne dono padosiyon se barabar overlap karta hai, aur chhe mil kar ek continuous π system ban jaate hain, plane ke upar electron density ki ek ring aur neeche ek matching ring.

Is tarah chhe nuclei par faile electrons delocalised hain, aur zyada nuclei ka attraction unki energy kam kar deta hai. Do measurements is picture ka saath dete hain. X-ray diffraction ek flat ring dikhata hai jiske chhe C–C bonds sab 139 pm ke hain, single bond (154 pm) aur double bond (134 pm) ke beech, jabki fixed Kekulé ring mein do bond lengths hoti. Aur benzene teen aam double bonds wale ek kaalpanik cyclohexatriene se kaafi zyada stable hai (Exercise Q10 isko number deta hai). Attack karne ke liye koi isolated double bond na hone se benzene zyaadatar addition reagents ko nazarandaz kar deta hai.

4/4Delocalised π cloud; har C–C bond 139 pm.

Fig. 9.14Benzene chhe delocalised π electrons wala ek hybrid hai, do badalte structures nahi.NCERT Fig. 9.7 · p. 320

Step 1 Kekulé structure A dikhata hai, ek hexagon jiske alternate edges par double bonds hain. Step 2 Kekulé structure B dikhata hai, jismein double bonds baaki teen edges par khisak gaye hain, aur A aur B ke beech double-headed resonance arrow hai. Step 3 chhe khade p orbitals dikhata hai, hexagon ke har carbon par ek, jo dono padosiyon se overlap kar sakta hai. Step 4 resonance hybrid dikhata hai: andar circle wala hexagon, ring ke upar aur neeche pi cloud, aur label ki chhe ke chhe C–C bonds 139 pm ke hain, 154 pm aur 134 pm ke beech.

9.5.3 Aromaticity

Benzene original aromatic compound tha, lekin aaj yeh word kisi bhi ring system ke liye use hota hai, benzene ring ho ya na ho, jismein yeh teen features hon:

Planarity: saare ring atoms ek plane mein hon.
Ring ke around π electrons ka complete delocalisation, jiske liye har ring atom par ek p orbital chahiye.
$4 n + 2$ π electrons: ring mein 2, 6, 10, … π electrons hone chahiye ( $n = 0, 1, 2, \dots$ ). Yeh Hückel rule hai, German physicist Erich Hückel (1931) ke naam par.

Definition

Aromaticity

Aisi planar ring ki extra stability jiske π electrons poori tarah delocalised hon aur unki sankhya $4 n + 2$ ( $n = 0, 1, 2, \dots$ ) ho.

ExampleBenzene (6 π electrons, n = 1).

Table 9.5Hückel rule se rings ko test karna

Ring	Planar aur delocalised?	π electrons	Kya aromatic?
benzene	haan	6 (n = 1)	haan
cyclopropenyl cation, $C_{3} H_{3}^{+}$	haan	2 (n = 0)	haan
cyclopentadienyl anion, $C_{5} H_{5}^{-}$	haan	6 (n = 1)	haan
cyclooctatetraene dianion, $C_{8} H_{8}^{2 -}$	haan	10 (n = 2)	haan
naphthalene	haan	10 (n = 2)	haan
cyclobutadiene	haan	4	nahi (4n + 2 nahi)
cyclopentadiene	nahi ( $s p^{3}$ $C H_{2}$ )	4	nahi

9.5.4 Benzene ki Preparation

Industry benzene mainly coal tar se aur petroleum se, reforming dwara, leti hai (Section 9.2.3). Laboratory mein ise teen tarah se banaya ja sakta hai:

laal-garam iron tube mein ethyne ke cyclic polymerisation se (Section 9.4.4);
decarboxylation se: sodium benzoate ko soda lime ke saath garam karke;
phenol ke reduction se: phenol ki vapour ko garam zinc dust ke upar se guzaar kar.

Sodium benzoate se aur phenol se

\begin{aligned} C_{6} H_{5} C O O N a \\ + N a O H \overset{C a O, h e a t}{\to} \\ C_{6} H_{6} + N a_{2} C O_{3} \\ C_{6} H_{5} O H + Z n \\ \overset{h e a t}{\to} C_{6} H_{6} + Z n O \end{aligned}

9.5.5 Properties

Physical properties

Arenes non-polar aur zyaadatar colourless hote hain; halke wale liquids hain, bhaari wale solids, aur kai ki ek khaas smell hoti hai. Doosre hydrocarbons ki tarah yeh paani ke saath mix nahi hote lekin organic solvents mein mil jaate hain. Inmein carbon ka bada hissa hone se yeh dhuein wali, kaalikh bhari flame ke saath jalte hain, jo laboratory mein arene ko alkane se alag pehchanne ka aasan tarika hai.

Chemical properties

Arenes ka pehchaan wala reaction electrophilic substitution hai: ek electrophile ring ke hydrogen ki jagah le leta hai, aur aromatic ring bina badle bach jaati hai. Addition aur oxidation sirf khaas conditions mein hote hain. Aam substitutions yeh hain:

Nitration. Benzene ko concentrated nitric aur sulfuric acids ke mixture (nitrating mixture) ke saath garam karne se nitrobenzene, $C_{6} H_{5} N O_{2}$ , milta hai.
Halogenation. Anhydrous $A l C l_{3}$ , $F e C l_{3}$ ya $F e B r_{3}$ jaise Lewis acid ke saath chlorine ya bromine haloarene deta hai, jaise bromobenzene, $C_{6} H_{5} B r$ .
Sulphonation. Fuming sulfuric acid (oleum) ke saath garam karne se ek hydrogen ki jagah $- S O_{3} H$ aa jaata hai, aur benzenesulfonic acid milta hai.
Friedel–Crafts alkylation. Anhydrous $A l C l_{3}$ ke saath alkyl halide ring par ek alkyl group laga deta hai.
Friedel–Crafts acylation. Anhydrous $A l C l_{3}$ ke saath acyl chloride (ya acid anhydride) ek acyl group, RCO–, laga deta hai, jisse aryl ketone milta hai.

tert-Butylbenzene aur 1-phenylpropan-1-one

\begin{aligned} C_{6} H_{6} + (C H_{3})_{3} C C l \\ \overset{a n h y d \cdot A l C l_{3}}{\to} \\ C_{6} H_{5} C (C H_{3})_{3} \\ + H C l \\ C_{6} H_{6} + C_{2} H_{5} C O C l \\ \overset{a n h y d \cdot A l C l_{3}}{\to} \\ C_{6} H_{5} C O C_{2} H_{5} \\ + H C l \end{aligned}

Substitution ek group par rukna zaroori nahi. Zyada reagent ho to ring hydrogens badalti rehti hai: excess chlorine aur $A l C l_{3}$ ke saath chhe ke chhe ja sakte hain, aur $C_{6} C l_{6}$ bachta hai.

Electrophilic substitution ka mechanism

Electrophilic substitution ( $S_{E}$ ) teen steps mein hota hai (Fig. 9.15): (a) electrophile banta hai; (b) woh ring par attack karta hai, jisse carbocation intermediate banta hai; (c) intermediate ek proton kho deta hai.

Definition

Electrophilic substitution

Aisa reaction jismein ek electrophile aromatic ring par kisi atom, aam taur par hydrogen, ko σ-complex ke raaste replace karta hai, taaki ring aromatic bani rahe.

ExampleBenzene ka nitration.

(a) Electrophile banana. Teen reactions mein yeh kaam Lewis acid karta hai: anhydrous $A l C l_{3}$ chlorine, alkyl chloride ya acyl chloride se chloride ion chheen leta hai, aur $C l^{+}$ , $R^{+}$ ya acylium ion $R C O^{+}$ bachta hai, jaise $C l_{2} + A l C l_{3} \overset{}{\to} C l^{+} + [A l C l_{4}]^{-}$ . Nitration mein nitronium ion, $N O_{2}^{+}$ , use hota hai, jo tab banta hai jab sulfuric acid nitric acid ko protonate karta hai:

Nitronium ion banana

\begin{aligned} H N O_{3} + H_{2} S O_{4} \overset{}{⇌} \\ H_{2} N O_{3}^{+} + H S O_{4}^{-} \\ H_{2} N O_{3}^{+} \overset{}{⇌} \\ N O_{2}^{+} + H_{2} O \end{aligned}

Nitric acid, jo aam taur par acid hai, yahan aur bhi strong sulfuric acid ke saamne base ki tarah kaam kar raha hai.

(b) σ-complex. Electrophile ek ring carbon se judta hai, jo $s p^{3}$ hybridised ho jaata hai aur uspar H aur E dono hote hain. Peeche bacha positive charge resonance se baaki ring carbons mein share hota hai; yeh carbocation arenium ion, ya σ-complex, hai. Kyunki $s p^{3}$ carbon ke paas p orbital nahi hai, isliye ring ka π system us point par toot jaata hai, aur intermediate ab aromatic nahi rehta aur uski energy zyada hoti hai.

(c) Proton ka nikalna. Step (a) se bacha anion, nitration ke baad $H S O_{4}^{-}$ ya $A l C l_{3}$ -catalysed reaction ke baad $[A l C l_{4}]^{-}$ , $s p^{3}$ carbon se proton kheench leta hai. Uske do bonding electrons wapas ring mein aa jaate hain aur aromaticity laut aati hai. Wahi aromatic stability wapas paane ki wajah se benzene addition ki jagah substitution karta hai.

3/4Positive charge paanch carbons par fail jaata hai; aromaticity khatam ho jaati hai.

Fig. 9.15Electrophile bana, σ-complex bana, proton nikla: ring aromatic bani rehti hai.NCERT p. 323

Step 1 dikhata hai ki Br2 aur FeBr3 se Br+ aur FeBr4− bante hain. Step 2 dikhata hai ki Br+ benzene ring par attack karke ek carbon se judta hai, jispar ab H aur Br dono hain. Step 3 sigma complex ko ek tooti ring ki tarah dikhata hai jismein plus sign baaki paanch carbons par faila hai, aur us carbon ko sp3 label karta hai. Step 4 dikhata hai ki FeBr4− proton le leta hai, jisse bromobenzene, HBr aur wapas FeBr3 milte hain, aur poori aromatic ring laut aati hai.

Addition. Benzene se zabardasti addition karaya ja sakta hai, lekin sirf alkene se kahin zyada sakht conditions mein. High temperature aur pressure par nickel ke upar hydrogen ring ko saturate karke cyclohexane bana deti hai, aur ultraviolet light mein chlorine ke teen molecules add hokar benzene hexachloride (BHC), $C_{6} H_{6} C l_{6}$ , banate hain; iska ek isomer insecticide lindane tha, jise gammaxane bhi kehte hain.

Addition ke liye sakht conditions chahiye

\begin{aligned} C_{6} H_{6} + 3 H_{2} \\ \to_{h i g h T, p}^{N i} C_{6} H_{12} \\ C_{6} H_{6} + 3 C l_{2} \\ \overset{U V}{\to} C_{6} H_{6} C l_{6} \end{aligned}

Combustion. Benzene hawa mein kaalikh bhari flame ke saath jalta hai, $C_{6} H_{6} + \frac{15}{2} O_{2} \overset{}{\to} 6 C O_{2} + 3 H_{2} O$ . Kisi bhi hydrocarbon ke liye:

Hydrocarbon ka complete combustion

\begin{aligned} C_{x} H_{y} + (x + \frac{y}{4}) O_{2} \\ ⟶ x C O_{2} + \frac{y}{2} H_{2} O \end{aligned}

(9.83)

9.5.6 Monosubstituted benzene mein functional group ka directive influence

Toluene ka nitration karo to zyaadatar 2- aur 4-nitrotoluene milte hain; nitrobenzene ka nitration karo to zyaadatar 1,3-dinitrobenzene milta hai. Ring par pehle se maujood group, na ki aane wala electrophile, tay karta hai ki doosra group kahan jaayega aur kitni tezi se. Is steering ko substituent ka directive influence kehte hain (Fig. 9.16).

Definition

Directive influence

Benzene ring par pehle se maujood substituent ka control is par ki naya electrophile kahan (ortho/para ya meta) aur kitni tezi se substitute karega.

Example $- O H$ ortho/para direct karta hai; $- N O_{2}$ meta direct karta hai.

Ortho aur para directors. Phenol mein oxygen ka ek lone pair ring ke saath share hota hai. Resonance structures banane par negative charge C2, C4 aur C6, yaani ortho aur para carbons, par aata hai, lekin C3 ya C5 par kabhi nahi, isliye electrophiles mainly ortho aur para par jaate hain. Poori ring bhi benzene se zyada electron-rich ho jaati hai aur tez react karti hai, bhale hi electronegative oxygen σ bond ke zariye kuch density wapas kheenchta hai (–I effect): resonance ka push jeet jaata hai. Aise groups activating hain. Alkyl groups (–CH₃, –C₂H₅), alkoxy groups (–OCH₃) aur nitrogen groups –NH₂, –NHR aur –NHCOCH₃ bhi aisa hi karte hain.

Halogens beech mein hain. Inka resonance donation weak hai, lekin phir bhi ortho aur para attack ko favour karta hai, jaise chlorobenzene mein. Lekin overall electron density ki ladaai inka strong –I effect jeet jaata hai, isliye ring benzene se kam reactive hoti hai: halogens deactivating ortho/para directors hain.

Meta directors. –CHO, –COR, –COOH, –COOR, –CN, –SO₃H aur –NO₂ jaise groups ring se electrons kheenchte hain, σ bond ke zariye bhi aur resonance se bhi. Nitrobenzene ke resonance structures ortho aur para carbons par positive charge rakhte hain. Poori ring deactivate ho jaati hai, lekin meta positions sabse kam electron-poor hain, isliye electrophiles wahan attack karte hain.

Compare

Teen tarah ke substituents

Activating, ortho/para

–OH, –OCH₃
–NH₂, –NHR, –NHCOCH₃
–CH₃, –C₂H₅

Deactivating, ortho/para

–F, –Cl, –Br, –I

Deactivating, meta

–CHO, –COR
–COOH, –COOR
–CN, –SO₃H, –NO₂

2/3Withdrawal: ortho aur para par δ+, isliye attack meta par hota hai; ring deactivated.

Fig. 9.16Ring par pehle se maujood group tay karta hai ki agla group kahan jaayega.NCERT p. 324

Ek benzene ring jiske top par ek substituent hai aur uski ortho, meta aur para positions labelled hain. Step 1, OH group ke saath, do ortho carbons aur para carbon ko delta-minus signs se mark karta hai aur ring mein donation ka arrow dikhata hai: ortho/para, activating. Step 2, NO2 group ke saath, ortho aur para carbons ko delta-plus signs se mark karta hai aur aane wale electrophile ko do meta carbons ki taraf point karta hai: meta, deactivating. Step 3, Cl atom ke saath, inductive effect ke liye withdrawal arrow dikhata hai lekin phir bhi ortho aur para ko attack sites mark karta hai: ortho/para, deactivating.

9.6 Carcinogenicity aur Toxicity

1775 mein London ke surgeon Percivall Pott ne dekha ki chimney saaf karne walon ko aksar cancer ho jaata tha. Baad mein kaalikh mein iske zimmedaar polynuclear aromatic hydrocarbons (PAHs) paaye gaye, yaani aise compounds jinmein do se zyada benzene rings judi (fused) hoti hain. Kai PAHs carcinogenic (cancer karne wale) hain. Yeh tab bante hain jab bhi organic matter adhoora jalta hai: tobacco ke dhuein mein, gaadiyon ke exhaust mein, coal, lakdi aur gobar ke dhuein mein, aur jale hue khaane par. Body ke andar enzymes inhe reactive compounds mein badal dete hain jo DNA se judkar use nuksaan pahunchate hain, aur isse cancer shuru ho sakta hai.

Jaane-maane examples hain benzo[a]pyrene, jismein paanch fused rings hain aur jo cigarette ke dhuein aur kaalikh mein hota hai; dibenz[a,h]anthracene, jismein bhi paanch rings hain; aur 3-methylcholanthrene, jo laboratories mein tumours study karne ke liye use hota hai (Fig. 9.17). Benzene khud bhi toxic hai: lambe samay tak exposure, jaise kaam par petrol vapour ya solvent fumes, bone marrow ko nuksaan pahunchata hai aur leukaemia kar sakta hai.

Fig. 9.17Adhoora jalna PAHs banata hai; body mein activate hone ke baad yeh DNA se judte hain.NCERT p. 325

Arrows se jude teen panels. Left mein ek flame jiske upar dhuan hai, label adhoora jalna. Beech mein benzo[a]pyrene ki paanch fused hexagonal rings, label 5 fused rings. Right mein DNA double helix jismein ek cross wahan mark karta hai jahan reactive hydrocarbon judta hai.

Quick check

2 mein se 1

Polynuclear aromatic hydrocarbons mainly kis se bante hain?

methane ka complete combustionbenzene ka hydrogenationorganic matter ka incomplete combustionethene ka polymerisation

Answer dekho

Answer (C) organic matter ka incomplete combustion

Tobacco, coal, lakdi ya fuel ka dhuein wala, kam oxygen mein jalna fused-ring hydrocarbons banata hai. Complete combustion sirf carbon dioxide aur paani deta hai.

Recap

Summary aur key points

Hydrocarbons mein sirf carbon aur hydrogen hote hain; yeh hamare main fuels hain aur plastics, solvents aur medicines ka raw material. Yeh saturated, unsaturated ya aromatic hote hain (Section 9.1).
Alkanes, $C_{n} H_{2 n + 2}$ , mein $s p^{3}$ carbons hote hain; size ke saath chain isomers tezi se badhte hain, aur IUPAC names sabse lambi chain, sabse kam locants aur alphabetical order follow karte hain (Section 9.2.1).
Alkanes hydrogenation se, alkyl halides ke reduction (Zn/H⁺) se, Wurtz reaction se, soda lime ke saath decarboxylation se aur Kolbe electrolysis se bante hain (Section 9.2.2).
Alkane boiling points size ke saath badhte hain aur branching ke saath ghatte hain. Alkanes free-radical halogenation (3° > 2° > 1° H), combustion, controlled oxidation, isomerisation, aromatization, steam reforming aur cracking karte hain (Section 9.2.3).
C–C bond ke around rotation se conformations milte hain; staggered ethane eclipsed se lagbhag 12.5 kJ mol⁻¹ zyada stable hai, jo Sawhorse aur Newman projections mein dikhaya jaata hai (Section 9.2.4).
C=C bond ek σ bond aur ek kamzor π bond hai; khule π electrons electrophiles ko attract karte hain (Section 9.3.1).
Alkenes chain, position aur geometrical isomerism dikhate hain; cis–trans isomers ke liye har doubly bonded carbon par do alag groups chahiye (Section 9.3.3).
Alkenes alkynes (Lindlar: cis; Na/NH₃: trans), alkyl halides, vicinal dihalides aur alcohols se bante hain (Section 9.3.4).
Alkenes $H_{2}$ , halogens, HX (zyada stable carbocation ke zariye Markovnikov; peroxide ke saath HBr ke liye anti-Markovnikov), $H_{2} S O_{4}$ aur paani add karte hain; Baeyer's reagent aur bromine C=C ka test hain; ozonolysis use locate karta hai; alkenes polymerise hote hain (Section 9.3.5).
Alkynes, $C_{n} H_{2 n - 2}$ , linear hain ( $s p$ , ek σ + do π). Terminal ≡C–H acidic hai; alkynes reagent ke do molecules add karte hain, hydrate hokar carbonyl compounds dete hain aur trimerise hokar benzene banate hain (Section 9.4.4).
Benzene chhe delocalised π electrons aur barabar 139 pm bonds wala resonance hybrid hai; aromatic rings planar, poori tarah delocalised hoti hain aur unmein 4n + 2 π electrons hote hain (Section 9.5.3).
Arenes σ-complex ke zariye electrophilic substitution (nitration, halogenation, sulphonation, Friedel–Crafts) karte hain, aur addition sirf sakht conditions mein (Section 9.5.5).
Substituents orientation aur rate tay karte hain: –OH, –NH₂ aur –CH₃ activate karte hain aur ortho/para direct karte hain; halogens deactivate karte hain lekin ortho/para direct karte hain; –NO₂, –CHO aur –COOH deactivate karte hain aur meta direct karte hain (Section 9.5.6).
Benzene aur do se zyada fused rings wale polynuclear hydrocarbons, jo incomplete combustion se bante hain, toxic aur carcinogenic hain (Section 9.6).

Practice · 25 questions

Practice questions answers ke saath (NCERT “Exercises”)

Short answerEasyNCERT Exercises 9.1
Jab light mein ethane ka chlorination kiya jaata hai, to products mein thoda butane bhi milta hai. Samjhao ki yeh kaise banta hai.
Solution dikhao
AnswerTermination step mein do ethyl radicals jud jaate hain.
Initiation: $C l_{2} \overset{}{\to} 2 C l^{∙}$ .
Propagation: $C l^{∙}$ ethane se H leta hai, jisse HCl aur ek ethyl radical, $C_{2} H_{5}^{∙}$ , banta hai, jo $C l_{2}$ se Cl leta hai.
Termination: do ethyl radicals milte hain, $2 C_{2} H_{5}^{∙} \overset{}{\to} C_{4} H_{10}$ . Butane pehchaan wala by-product hai, bilkul waise hi jaise methane ke liye ethane.
2
Short answerEasyNCERT Exercises 9.2
In compounds ke IUPAC naam do:
1. $(C H_{3})_{2} C = C H C H_{2} C H_{3}$
  Solution dikhao
  Answer2-methylpent-2-ene
  Paanch-carbon chain, branched end se C2 par C=C, C2 par methyl.
2. $H C \equiv C - C H = C H - C H_{3}$
  Solution dikhao
  Answerpent-3-en-1-yne
  Alkyne wale end se number karne par set {1, 3} milta hai; doosre end se {2, 4}. Chhota set jeetta hai; -ene ko -yne se pehle likhte hain.
3. $C_{6} H_{5} C H_{2} C H = C H C H_{3}$
  Solution dikhao
  Answer1-phenylbut-2-ene
  Chaar-carbon chain jismein C=C kisi bhi end se C2 par hai; tie todne ke liye phenyl group ko locant 4 ki jagah 1 diya jaata hai.
4. $C H_{3} C H_{2} C H (C H_{3})^{-}$ $C H_{2} C H (C_{2} H_{5}) C H_{2} C H_{3}$
  Solution dikhao
  Answer3-ethyl-5-methylheptane
  Saat-carbon chain jiske substituents kisi bhi end se 3 aur 5 par hain; alphabet mein ethyl pehle aata hai, isliye use 3 milta hai.
3
Short answerMediumNCERT Exercises 9.3
$C_{4} H_{6}$ ke un saare open-chain isomers ke structures aur IUPAC naam likho jinmein hai:
1. ek triple bond
  Solution dikhao
  Answerbut-1-yne aur but-2-yne
  $H C \equiv C C H_{2} C H_{3}$ (but-1-yne) aur $C H_{3} C \equiv C C H_{3}$ (but-2-yne), jo position isomers hain.
2. do double bonds
  Solution dikhao
  Answerbuta-1,3-diene aur buta-1,2-diene
  $C H_{2} = C H - C H = C H_{2}$ (buta-1,3-diene) aur $C H_{2} = C = C H - C H_{3}$ (buta-1,2-diene).
4
Short answerEasyNCERT Exercises 9.4
Inke ozonolysis ke products ke naam do:
1. oct-4-ene
  Solution dikhao
  Answerbutanal (2 mol)
  $C_{3} H_{7} C H = C H C_{3} H_{7}$ toot kar do $C_{3} H_{7} C H O$ deta hai.
2. 2-methylpent-1-ene
  Solution dikhao
  Answermethanal aur pentan-2-one
  $C H_{2} =$ se HCHO milta hai; doosre carbon se $C H_{3} C O C_{3} H_{7}$ .
3. 3-methylpent-2-ene
  Solution dikhao
  Answerethanal aur butan-2-one
  $C H_{3} C H =$ se $C H_{3} C H O$ milta hai; $= C (C H_{3}) C_{2} H_{5}$ se $C H_{3} C O C_{2} H_{5}$ .
4. 1-phenylprop-1-ene
  Solution dikhao
  Answerbenzaldehyde aur ethanal
  $C_{6} H_{5} C H =$ se $C_{6} H_{5} C H O$ milta hai; $= C H C H_{3}$ se $C H_{3} C H O$ .
Short answerMediumNCERT Exercises 9.5
Alkene B ka ozonolysis propanone aur butanal deta hai. B pehchano aur uska naam do.
Solution dikhao
Answer2-methylhex-2-ene
Propanone $(C H_{3})_{2} C =$ deta hai aur butanal $= C H C H_{2} C H_{2} C H_{3}$ .
$\begin{aligned} (C H_{3})_{2} C = C H^{-} \\ C H_{2} C H_{2} C H_{3} \end{aligned}$
C=C se hokar jaane wali sabse lambi chain mein chhe carbons hain; branched end se number karne par C=C aur methyl C2 par aate hain: 2-methylhex-2-ene.
NumericalMediumNCERT Exercises 9.6
Ek alkene X mein paanch C–C σ bonds, baarah C–H σ bonds aur ek C–C π bond hai. Ozonolysis par yeh 58 u molar mass wale ek hi aldehyde ke do moles deta hai. X ka naam do.
Solution dikhao
Answerhex-3-ene
Open chain mein baarah C–H bonds aur ek C=C: $C_{6} H_{12}$ , jismein chhe-carbon chain par paanch C–C σ bonds hain.
Aldehyde $C_{n} H_{2 n} O$ ka $M = 14 n + 16 = 58$ , isliye $n = 3$ : propanal.
Do propanal units ko unke carbonyl carbons par jodne se $C_{2} H_{5} C H = C H C_{2} H_{5}$ milta hai: hex-3-ene.
Short answerMediumNCERT Exercises 9.7
Ek unknown alkene ka ozonolysis butanone aur methanal deta hai. Uska structure pehchano.
Solution dikhao
Answer2-methylbut-1-ene
Butanone, $C H_{3} C O C_{2} H_{5}$ , $(C H_{3}) (C_{2} H_{5}) C =$ deta hai; methanal $= C H_{2}$ deta hai.
Alkene $C H_{2} = C (C H_{3}) C_{2} H_{5}$ , yaani 2-methylbut-1-ene, hai.
8
Short answerEasyNCERT Exercises 9.8
Inke complete combustion ke balanced equations likho:
1. heptane
  Solution dikhao
  $\begin{aligned} C_{7} H_{16} + 11 O_{2} \overset{}{\to} \\ 7 C O_{2} + 8 H_{2} O \end{aligned}$
2. propene
  Solution dikhao
  $\begin{aligned} 2 C_{3} H_{6} + 9 O_{2} \overset{}{\to} \\ 6 C O_{2} + 6 H_{2} O \end{aligned}$
3. but-1-yne
  Solution dikhao
  $\begin{aligned} 2 C_{4} H_{6} + 11 O_{2} \overset{}{\to} \\ 8 C O_{2} + 6 H_{2} O \end{aligned}$
4. ethylbenzene
  Solution dikhao
  $\begin{aligned} 2 C_{8} H_{10} + 21 O_{2} \overset{}{\to} \\ 16 C O_{2} + 10 H_{2} O \end{aligned}$
Short answerMediumNCERT Exercises 9.9
Pent-2-ene do geometrical isomers ke roop mein exist karta hai. Unhe sketch karo aur reason ke saath predict karo ki kaun zyada temperature par boil hoga.
Solution dikhao
Answercis (thoda zyada)
cis: $C H_{3}$ aur $C_{2} H_{5}$ C=C ki ek hi side par; trans: opposite sides par.
Cis isomer ka chhota sa net dipole moment hai, jabki trans isomer mein bond dipoles lagbhag cancel ho jaate hain. Extra dipole–dipole attraction cis-pent-2-ene ko thoda zyada boiling point deta hai (lagbhag 37 °C vs 36 °C).
NumericalMediumNCERT Exercises 9.10
Cyclohexene (ek C=C) ka hydrogenation 120 kJ mol⁻¹ chhodta hai. Benzene ka cyclohexane tak hydrogenation sirf 208 kJ mol⁻¹ chhodta hai. Benzene teen isolated double bonds wali ring se kitna zyada stable hai?
kJ/mol
Solution dikhao
Teen isolated C=C bonds lagbhag 360 kJ/mol chhodte. Benzene 152 kJ/mol kam chhodta hai kyunki uske delocalised π electrons pehle se kam energy par hain. Yeh resonance (delocalisation) energy uski asaadharan stability ko samjhati hai.
Short answerEasyNCERT Exercises 9.11
Ring ke aromatic hone ki conditions batao, aur unse decide karo ki cycloheptatrienyl cation, $C_{7} H_{7}^{+}$ , aromatic hai ya nahi.
Solution dikhao
AnswerAromatic hai: planar, delocalised, 6 π electrons.
Conditions: planar ring; har ring atom par p orbital taaki π electrons poori tarah delocalised hon; aur 4n + 2 π electrons.
$C_{7} H_{7}^{+}$ : ek plane mein saat $s p^{2}$ carbons (positive carbon ke paas khaali p orbital hai), teen C=C bonds jo 6 π electrons dete hain, isliye n = 1. Yeh aromatic hai.
12
Short answerMediumNCERT Exercises 9.12
Inmein se koi bhi aromatic nahi hai. Har ek ke liye batao ki kaun si condition fail hoti hai.
1. cycloheptatriene, C₇H₈
  Solution dikhao
  Ek ring carbon $s p^{3}$ $C H_{2}$ hai jiske paas p orbital nahi hai, isliye delocalisation complete nahi hai.
2. cyclopentadienyl cation, C₅H₅⁺
  Solution dikhao
  Yeh planar aur poori tarah conjugated hai lekin ismein sirf 4 π electrons hain, jo 4n + 2 nahi hai.
3. cycloheptatrienyl anion, C₇H₇⁻
  Solution dikhao
  Ismein 8 π electrons hain, jo 4n + 2 nahi hai.
13
Short answerMediumNCERT Exercises 9.13
Benzene se shuru karke inka synthesis outline karo:
1. m-bromonitrobenzene
  Solution dikhao
  Pehle nitration karo ( $H N O_{3}$ / $H_{2} S O_{4}$ ); phir –NO₂ bromine ( $B r_{2}$ / $F e B r_{3}$ ) ko meta position par direct karta hai.
2. p-bromotoluene
  Solution dikhao
  Pehle methylation karo ( $C H_{3} C l$ / $A l C l_{3}$ ), phir bromination ( $B r_{2}$ / $F e B r_{3}$ ); –CH₃ o/p direct karta hai, aur p isomer ko alag kar liya jaata hai.
3. m-nitroacetophenone
  Solution dikhao
  Pehle acylation karo ( $C H_{3} C O C l$ / $A l C l_{3}$ ), phir nitration; –COCH₃ meta direct karta hai. (Nitrobenzene Friedel–Crafts reaction nahi karta.)
4. benzophenone, C₆H₅COC₆H₅
  Solution dikhao
  Benzoyl chloride, $C_{6} H_{5} C O C l$ , aur anhydrous $A l C l_{3}$ ke saath Friedel–Crafts acylation.
Short answerEasyNCERT Exercises 9.14
2,2,4-trimethylhexane, $(C H_{3})_{3} C C H_{2} C H (C H_{3}) C_{2} H_{5}$ , mein kitne 1°, 2°, 3° aur 4° carbons hain, aur har tarah ke carbon par kitne H atoms hain?
Solution dikhao
Answer1°: 5 (15 H); 2°: 2 (4 H); 3°: 1 (1 H); 4°: 1 (0 H)
1°: C2 par teen methyls, C4 par methyl aur C6 = 5 carbons, har ek par 3 H = 15 H.
2°: C3 aur C5 = 2 carbons, 4 H. 3°: C4, 1 H. 4°: C2, koi H nahi.
Check: 9 carbons aur 20 hydrogens, $C_{9} H_{20}$ .
15
Short answerEasyNCERT Exercises 9.15
Heptane, 2-methylhexane aur 2,2-dimethylpentane ko boiling point ke ghatte order mein lagao, aur samjhao.
1. 2-methylhexane
2. 2,2-dimethylpentane
3. heptane
Solution dikhao
Teenon C₇H₁₆ hain. Zyada branching molecule ko zyada compact banati hai, jisse contact area aur dispersion forces kam ho jaate hain, isliye boiling point girta hai: heptane > 2-methylhexane > 2,2-dimethylpentane.
Long answerMediumNCERT Exercises 9.16
Bina peroxide ke but-1-ene aur HBr se 2-bromobutane milta hai; benzoyl peroxide ke saath product 1-bromobutane hai. Is badlav ko samjhao aur radical chain steps likho.
Solution dikhao
AnswerCarbocation path 2-bromobutane deta hai; radical path 1-bromobutane deta hai.
Bina peroxide ke: $H^{+}$ C1 par add hota hai, jisse secondary carbocation $C_{2} H_{5} C^{+} H C H_{3}$ banta hai; phir $B r^{-}$ se 2-bromobutane milta hai (Markovnikov).
Peroxide ke saath iski jagah radical chain chalti hai:
$\begin{aligned} (C_{6} H_{5} C O O)_{2} \overset{}{\to} \\ 2 C_{6} H_{5}^{∙} + 2 C O_{2} \\ C_{6} H_{5}^{∙} + H B r \overset{}{\to} \\ C_{6} H_{6} + B r^{∙} \\ C H_{2} = C H C_{2} H_{5} \\ + B r^{∙} \overset{}{\to} \\ B r C H_{2} C^{∙} H C_{2} H_{5} \\ + H B r \overset{}{\to} \\ B r C H_{2} C H_{2} C_{2} H_{5} \\ + B r^{∙} \end{aligned}$
Br• C1 par add hota hai taaki radical secondary C2 par rahe, jo zyada stable option hai; product 1-bromobutane hai.
Long answerHardNCERT Exercises 9.17
1-ethyl-2-methylbenzene ke ozonolysis ke products har Kekulé structure se predict karo. Observed mixture Kekulé ke khisakte double bonds wale idea ka saath kaise dega?
Solution dikhao
AnswerChaar products, jinmein se do sirf alag-alag Kekulé structures se hi aa sakte hain.
C1=C2 wala structure: fragments C2–C3, C4–C5, C6–C1 se 2-oxopropanal ( $C H_{3} C O C H O$ ), ethanedial ( $O H C C H O$ ) aur 2-oxobutanal ( $C_{2} H_{5} C O C H O$ ) milte hain.
C2=C3 wala structure: fragments C1–C2, C3–C4, C5–C6 se pentane-2,3-dione ( $C_{2} H_{5} C O C O C H_{3}$ ) aur do ethanedial milte hain.
Chaaron compounds ka milna dikhata hai ki dono arrangements contribute karte hain: double bonds fixed nahi hain, jaisa Kekulé ne propose kiya tha (ab resonance se samjhaya jaata hai).
18
Short answerEasyNCERT Exercises 9.18
Propane, propene aur propyne ko sabse zyada se sabse kam acidic ke order mein rank karo (har ek ka sabse acidic hydrogen socho) aur ranking samjhao.
1. propyne
2. propane
3. propene
Solution dikhao
Sabse acidic hydrogens $s p$ (propyne, 50 % s), $s p^{2}$ (propene, 33 %) aur $s p^{3}$ carbons (propane, 25 %) par hain. Zyada s character C–H electrons ko carbon ke zyada paas rakhta hai, isliye proton aasani se nikalta hai: propyne > propene > propane.
Short answerMediumNCERT Exercises 9.19
Benzene $B r_{2}$ / $F e B r_{3}$ ke saath addition ki jagah substitution se react karta hai, phir bhi aam conditions mein $O H^{-}$ jaise nucleophiles se react nahi karta. Dono observations samjhao.
Solution dikhao
AnswerElectron-rich π cloud electrophiles ko attract karta hai aur nucleophiles ko repel; substitution ring ko aromatic rakhta hai.
Ring ke upar aur neeche ke chhe delocalised π electrons benzene ko electron-rich banate hain, isliye yeh electron dhoondhne wale electrophiles ko attract karta hai aur electron-rich nucleophiles ko repel karta hai.
Electrophile add hone ke baad H⁺ ka nikalna stable aromatic ring ko wapas la deta hai, jabki addition use khatam kar deta. Isliye substitution jeetta hai.
20
Short answerEasyNCERT Exercises 9.20
Tum benzene kaise banaoge:
1. calcium carbide se
  Solution dikhao
  Paani daal kar ethyne lo, phir use 873 K par laal-garam iron tube se guzaaro.
2. 1,2-dibromoethane se
  Solution dikhao
  Alcoholic KOH, phir $N a N H_{2}$ , se ethyne milta hai; phir laal-garam iron tube se benzene.
3. phenol se
  Solution dikhao
  Phenol ki vapour ko garam zinc dust ke upar se guzaaro.
Short answerMediumNCERT Exercises 9.21
Kai alkenes hydrogenate hone par 3-methylpentane dete hain. Un sabko banao.
Solution dikhao
Answer3 structural isomers (ek ke cis/trans forms ke saath)
3-Methylpent-1-ene, $C H_{2} = C H C H (C H_{3}) C_{2} H_{5}$ .
3-Methylpent-2-ene, $C H_{3} C H = C (C H_{3}) C_{2} H_{5}$ (cis aur trans forms).
2-Ethylbut-1-ene, $C H_{2} = C (C_{2} H_{5})_{2}$ , jismein double bond branch wale carbon tak hai.
22
Short answerMediumNCERT Exercises 9.22
Electrophilic substitution mein har teen ke group ko sabse tez se sabse dheeme ke order mein rank karo:
1. (a)
  benzene, phenol, chlorobenzene
  benzene
  phenol
  chlorobenzene
  Answer dekho
  Answer
  phenol
  benzene
  chlorobenzene
  –OH strongly activate karta hai; –Cl thoda deactivate karta hai.
2. (b)
  nitrobenzene, 1,3-dinitrobenzene, chlorobenzene
  1,3-dinitrobenzene
  chlorobenzene
  nitrobenzene
  Answer dekho
  Answer
  chlorobenzene
  nitrobenzene
  1,3-dinitrobenzene
  –Cl sabse kam deactivate karta hai; har –NO₂ strongly deactivate karta hai.
Short answerEasyNCERT Exercises 9.23
Benzene, ethylbenzene aur benzoic acid ka same conditions mein nitration kiya jaata hai. Kaun sabse tez react karta hai? Samjhao.
Solution dikhao
AnswerEthylbenzene
Ethyl group ring ko electron density donate karta hai (+I effect aur hyperconjugation), jisse ring activate hoti hai, isliye ethylbenzene ka nitration sabse tez hota hai. –COOH electrons kheenchta hai, isliye benzoic acid ka nitration sabse dheema hota hai.
Short answerEasyNCERT Exercises 9.24
Chloromethane ke saath Friedel–Crafts methylation ke liye anhydrous $A l C l_{3}$ hi akela catalyst nahi hai. Ek aur Lewis acid ka naam do jo kaam karta hai aur dikhao ki woh electrophile kaise banata hai.
Solution dikhao
AnswerAnhydrous $F e C l_{3}$
Anhydrous iron(III) chloride ek chloride ion accept karta hai: $C H_{3} C l + F e C l_{3}$ $\overset{}{\to} C H_{3}^{+} + [F e C l_{4}]^{-}$ . (Asal mein $C H_{3}$ –Cl bond poori tarah tootta nahi, balki strongly polarise hota hai.)
Short answerMediumNCERT Exercises 9.25
Pentane banane ke liye 1-bromopropane aur bromoethane ka mixture sodium ke saath achha tarika kyun nahi hai? Products ke naam do.
Solution dikhao
AnswerButane, pentane aur hexane saath bante hain.
Sodium kinhi bhi do alkyl groups ko jodta hai: ethyl + ethyl se butane, ethyl + propyl se pentane aur propyl + propyl se hexane milta hai.
Pentane product ka sirf ek hissa hai aur use alag karna padta hai, isliye Wurtz sirf symmetrical (even-carbon) alkanes ke liye use hota hai.

Apna NCERT exercise question dhoondo

Hamare practice questions ncert.ai ke liye likhe gaye hain aur NCERT exercises ko follow karte hain. Apni textbook ke question se match karne wala question dhoondo; uska answer uske saath hai.

Tumhari NCERT textbook mein	Yahan practice question
NCERT Exercises 9.1	Practice Q1
NCERT Exercises 9.2	Practice Q2
NCERT Exercises 9.3	Practice Q3
NCERT Exercises 9.4	Practice Q4
NCERT Exercises 9.5	Practice Q5
NCERT Exercises 9.6	Practice Q6
NCERT Exercises 9.7	Practice Q7
NCERT Exercises 9.8	Practice Q8
NCERT Exercises 9.9	Practice Q9
NCERT Exercises 9.10	Practice Q10
NCERT Exercises 9.11	Practice Q11
NCERT Exercises 9.12	Practice Q12
NCERT Exercises 9.13	Practice Q13
NCERT Exercises 9.14	Practice Q14
NCERT Exercises 9.15	Practice Q15
NCERT Exercises 9.16	Practice Q16
NCERT Exercises 9.17	Practice Q17
NCERT Exercises 9.18	Practice Q18
NCERT Exercises 9.19	Practice Q19
NCERT Exercises 9.20	Practice Q20
NCERT Exercises 9.21	Practice Q21
NCERT Exercises 9.22	Practice Q22
NCERT Exercises 9.23	Practice Q23
NCERT Exercises 9.24	Practice Q24
NCERT Exercises 9.25	Practice Q25

Quick check: MCQs

9.1 Classification2 questions
9.2.1 Nomenclature aur Isomerism3 questions
Carboxylic acids se3 questions
Chemical properties4 questions
Ethane ke conformations3 questions
Geometrical isomerism3 questions
Alcohols se acidic dehydration dwara3 questions
Chemical properties4 questions
Chemical properties4 questions
Benzene ki resonance aur stability3 questions
Electrophilic substitution ka mechanism4 questions
9.5.6 Monosubstituted benzene mein functional group ka directive influence3 questions
9.6 Carcinogenicity aur Toxicity2 questions

Glossary · 15

Key terms (English + Hindi)

alkaneऐल्केनailken: Ek saturated open-chain hydrocarbon, $C_{n} H_{2 n + 2}$ .Chapter mein pehli baar yahan aaya →
alkeneऐल्कीनailkeen: C=C double bond wala hydrocarbon; ek double bond ke liye $C_{n} H_{2 n}$ .Chapter mein pehli baar yahan aaya →
alkyneऐल्काइनailkain: C≡C triple bond wala hydrocarbon; ek triple bond ke liye $C_{n} H_{2 n - 2}$ .Chapter mein pehli baar yahan aaya →
areneऐरीनaireen: Aromatic ring, aam taur par benzene ring, wala hydrocarbon.Chapter mein pehli baar yahan aaya →
aromaticityऐरोमैटिकताaromaticata: 4n + 2 π electrons wali planar, poori tarah delocalised ring ki stability.

conformationसंरूपणsanrupan: Single bond ke around rotation se mila molecule ka arrangement, bina koi bond tode.Chapter mein pehli baar yahan aaya →

directive influence: Ring substituent ka control is par ki agla substitution kahan (o/p ya m) aur kitni tezi se hoga.Chapter mein pehli baar yahan aaya →

electrophileइलेक्ट्रॉनस्नेहीelectronsnehi: Electron dhoondhne wali species, jaise $H^{+}$ ya $N O_{2}^{+}$ .Chapter mein pehli baar yahan aaya →
electrophilic substitutionइलेक्ट्रॉनस्नेही प्रतिस्थापनelectronsnehi pratisthapan: σ-complex ke zariye electrophile dwara ring hydrogen ka replacement, jisse ring aromatic bani rehti hai.Chapter mein pehli baar yahan aaya →

free radicalमुक्त मूलकmukt moolak: Unpaired electron wala atom ya group, jo bond ke homolysis se banta hai.Chapter mein pehli baar yahan aaya →

geometrical isomerismज्यामितीय समावयवताjyamitiya samavayavta: C=C bond ke around groups ke alag arrangements se hone wali isomerism, jo restricted rotation ki wajah se hoti hai.Chapter mein pehli baar yahan aaya →

Markovnikov rule: Unsymmetrical alkene par H–X add karne mein H zyada hydrogens wale doubly bonded carbon par jaata hai.

ozonolysisओज़ोनी अपघटनozoni apghatan: Ozone aur phir Zn/H₂O se C=C bond ka tootna, jisse do carbonyl compounds milte hain.Chapter mein pehli baar yahan aaya →

peroxide effectपरॉक्साइड प्रभावparoxide prabhav: Peroxide ki maujoodgi mein unsymmetrical alkene par HBr ka anti-Markovnikov addition, radical chain dwara.Chapter mein pehli baar yahan aaya →

torsional strain: Paas wale atoms ke bonds ke beech ka repulsion jo eclipsed conformations ki energy badhata hai.Chapter mein pehli baar yahan aaya →

9.1 Classification

9.2 Alkanes

9.2.1 Nomenclature aur Isomerism

9.2.2 Preparation

Unsaturated hydrocarbons se

Alkyl halides se

Carboxylic acids se

9.2.3 Properties

Physical properties

Chemical properties

9.2.4 Conformations

Ethane ke conformations

9.3 Alkenes

9.3.1 Double Bond ka Structure

9.3.2 Nomenclature

9.3.3 Isomerism

Geometrical isomerism

9.3.4 Preparation

Alkynes se

Alkyl halides se

Vicinal dihalides se

Alcohols se acidic dehydration dwara

9.3.5 Properties

Physical properties

Chemical properties

9.4 Alkynes

9.4.1 Nomenclature aur Isomerism

9.4.2 Triple Bond ka Structure

9.4.3 Preparation

9.4.4 Properties

Physical properties

Chemical properties

9.5 Aromatic Hydrocarbon

9.5.1 Nomenclature aur Isomerism

9.5.2 Benzene ka Structure

Benzene ki resonance aur stability

9.5.3 Aromaticity

9.5.4 Benzene ki Preparation

9.5.5 Properties

Physical properties

Chemical properties

Electrophilic substitution ka mechanism

9.5.6 Monosubstituted benzene mein functional group ka directive influence

9.6 Carcinogenicity aur Toxicity

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Quick check: MCQs

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