Class 11 Chemistry · Chapter 9
Short answer:
Hydrocarbons — sirf carbon aur hydrogen se bane organic compounds — rationalised Class 11 Chemistry syllabus (2026-27) ka Chapter 9 hai, poore course ka last chapter. Teen types: alkanes (CnH2n+2, saturated, free-radical substitution), alkenes/alkynes (C=C / C≡C, unsaturated, electrophilic addition + Markovnikov's rule) aur aromatic hydrocarbons (benzene-type, electrophilic substitution). Yahan poora "hydrocarbons class 11 ncert solutions" style step-by-step working diya gaya hai.
Chapter 9 "Hydrocarbons" — rationalised 2026-27 Class 11 Chemistry syllabus ka last chapter — seedha Chapter 8 "Organic Chemistry: Some Basic Principles and Techniques" ka practical extension hai. Wahan IUPAC nomenclature, isomerism aur mechanism ki bhasha (inductive, resonance, electromeric effect) seekhi thi; yahan wahi bhasha real molecules — alkanes, alkenes, alkynes, benzene — pe apply hoti hai. Agar "class 11 chemistry organic chemistry basic principles and techniques notes" clear nahi hain, pehle unhe revise kar lo.
Ye chapter roz ki zindagi se juda hai — petrol-diesel-LPG se lekar plastics aur naphthalene tak, sab hydrocarbons hain. Exam ki drishti se teen alag mechanism types ek saath aate hain: free radical substitution (alkanes), electrophilic addition with Markovnikov's rule aur peroxide effect (alkenes/alkynes), aur electrophilic aromatic substitution with directive influence (benzene). Confuse yahin sabse zyada hota hai — kaunsa mechanism kaha lagta hai.
"class 11 chemistry ncert solutions pdf" ya "class 11 chemistry all chapters list ncert" dhoondh rahe ho to yaad rakho — "class 11 chemistry syllabus 2026-27 rationalised" me sirf 9 chapters hain, pehle 14 the. Hydrocarbons in 9 me 9th aur akhri chapter hai.
Chapter 9 Summary — 5 Minute Revision
Yeh chapter 5 hisson me organize hota hai:
- 9.1 Classification — saturated (alkanes), unsaturated (alkenes, alkynes), aromatic hydrocarbons.
- 9.2 Alkanes — IUPAC nomenclature, isomerism, ethane ki conformations (eclipsed/staggered), reactions: free radical halogenation, combustion, controlled oxidation, isomerization, aromatization, pyrolysis (cracking).
- 9.3 Alkenes — sp2 structure, geometrical (cis-trans/E-Z) isomerism, preparation, reactions: Markovnikov's rule, peroxide (Kharasch) effect, hydroboration-oxidation, ozonolysis, polymerization, Baeyer's test.
- 9.4 Alkynes — sp structure, terminal alkyne ki acidic nature, CaC2 se preparation, addition reactions (HX, Kucherov hydration, H2).
- 9.5 Aromatic Hydrocarbons — benzene resonance, Huckel's rule, electrophilic substitution mechanism (nitration, sulphonation, halogenation, Friedel-Crafts), directive influence, carcinogenicity.
In-Text Questions — Solutions
Following compounds ke IUPAC naam likho: (i) CH3-CH(CH3)-CH2-CH2-CH3 (ii) CH2=CH-CH(CH3)-CH3 (iii) CH≡C-CH2-CH3
Longest chain dhoondo jisme functional group (double/triple bond) shamil ho, lowest locants do.
(i) 5-carbon chain, C2 pe methyl → 2-methylpentane
(ii) 4-carbon chain, C1=C2 double bond, C3 pe methyl → 3-methylbut-1-ene
(iii) 4-carbon chain, C1≡C2 triple bond → but-1-yne
Hexane (C6H14) ke saare chain (structural) isomers likho, IUPAC naam ke saath.
Branching systematically try karo — total 5 isomers bante hain:
- CH3-CH2-CH2-CH2-CH2-CH3 — hexane
- 2-methylpentane
- 3-methylpentane
- 2,2-dimethylbutane
- 2,3-dimethylbutane
CH3-CH2-CH2-CH3 aur CH3-CH(CH3)-CH3 — ye pair kis type ke isomer hain? Ek aur pair CH2=CH-CH2-CH3 aur CH3-CH=CH-CH3 ka bhi bataiye.
Pehla pair: dono C4H10 (n-butane vs isobutane) hain — carbon skeleton alag hai → chain isomers.
Doosra pair: dono C4H8 hain, double bond ki position alag hai (but-1-ene vs but-2-ene) → position isomers.
Ek alkene A me 3 C-C sigma bonds, 8 C-H sigma bonds aur 1 C=C pi bond hai. Ozonolysis pe A do moles ek hi aldehyde deta hai jiska molar mass 44 u hai. A ka IUPAC naam do.
Molar mass 44 wala aldehyde = CH3CHO (acetaldehyde). Do mole same aldehyde milna symmetrical alkene batata hai:
CH3-CH=CH-CH3 --(O3/Zn-H2O)--> 2 CH3CHO
Sigma bond count check: C1-C2, C2-C3, C3-C4 = 3 C-C sigma; 8 H (3+1+1+3) ✓. Isliye A = but-2-ene.
Toluene, benzene, chlorobenzene, nitrobenzene ko electrophile ke saath reactivity ke ghatte hue order me lagao.
Ring pe electron density jitni zyada, electrophilic substitution utna aasan. CH3 activating (+I), Cl weakly deactivating, NO2 strongly deactivating (-M):
Toluene > Benzene > Chlorobenzene > Nitrobenzene
Benzene, m-dichlorobenzene aur mesitylene (1,3,5-trimethylbenzene) me se kaun Friedel-Crafts reaction sabse aasani se karega, aur kyun?
Friedel-Crafts ek electrophilic substitution hai — electron-rich ring fast react karti hai. Mesitylene me teen -CH3 groups (+I, activating) ring ki electron density kaafi badhate hain, jabki m-dichlorobenzene ke do -Cl (deactivating) ring ko electron-poor banate hain.
Order: mesitylene > benzene > m-dichlorobenzene — Friedel-Crafts sabse aasan mesitylene me.
Methane ki chlorination (CH4 + Cl2 --hν--> CH3Cl) ka free radical mechanism steps me likho.
Initiation:
Cl2 --hν--> 2 Cl•
Propagation:
CH4 + Cl• → CH3• + HCl
CH3• + Cl2 → CH3Cl + Cl•
Termination (radicals aapas me combine): Cl•+Cl•→Cl2; CH3•+CH3•→C2H6; CH3•+Cl•→CH3Cl
Wurtz reaction unsymmetrical ya odd-carbon alkane banane ke liye preferred kyu nahi hai?
Wurtz reaction: 2R-X + 2Na --dry ether--> R-R + 2NaX. Agar do alag alkyl halides (R-X aur R'-X) use karo to teen products ka mixture banta hai — R-R, R'-R', aur R-R' — jinhe separate karna mushkil hai. Isliye ye sirf symmetrical alkane (same R dono taraf, even carbon count) banane ke liye reliable hai.
Propyne (CH3-C≡CH) ke reactions likho: (a) HBr peroxide ke saath (b) H2O dilute H2SO4/HgSO4 ke saath.
(a) Peroxide effect (anti-Markovnikov, free radical mechanism) — Br terminal (more-H) carbon pe:
CH3-C≡CH + HBr --peroxide--> CH3-CH=CHBr
(b) Kucherov reaction — Markovnikov hydration, enol phir keto-form me tautomerise:
CH3-C≡CH + H2O --H2SO4/HgSO4--> [CH3-C(OH)=CH2] → CH3-CO-CH3 (acetone)
But-2-ene ke geometrical isomers draw karke E/Z naming do.
C2=C3 pe dono taraf CH3 aur H hain — do arrangement possible:
Dono CH3 same side → cis / (Z)-but-2-ene
CH3 opposite side → trans / (E)-but-2-ene
(Priority: CH3 > H dono carbons pe, isliye cis=Z, trans=E yahan match karte hain.)
Aniline/phenol me electrophilic substitution benzene se aasan kyun hai, jabki nitrobenzene me mushkil?
-NH2 aur -OH strong +M (electron-donating via lone pair resonance into ring) groups hain — ring electron-rich ho jaati hai, especially ortho/para positions pe — isliye substitution fast aur o,p-directed hota hai.
-NO2 strong -M/-I (electron-withdrawing) group hai — ring electron-poor ho jaati hai, isliye substitution slow (harsh conditions chahiye) aur meta-directed hota hai (meta position sabse kam deactivated rehta hai).
1-bromopropane alcoholic KOH ke saath react karta hai — major product kya banega aur kyun?
Alcoholic KOH elimination (dehydrohalogenation, E2) favour karta hai, substitution nahi. C2 se H aur C1 se Br nikalta hai:
CH3-CH2-CH2Br --alc. KOH--> CH3-CH=CH2 (propene) + KBr + H2O
Terminal halide hone se sirf ek hi elimination direction possible hai, isliye Saytzeff choice yahan apply nahi hoti.
Poore Class 11 Chemistry ke handwritten colour notes
IITian & district toppers ke banaye short notes — revision-ready, diagram ke saath. Board se pehle poora syllabus 3 din me revise.
Exercise Questions — Solutions (Q1–Q19)
Hydrocarbons kya hain? Inka classification examples ke saath samjhao.
Hydrocarbons wo organic compounds hain jo sirf C aur H atoms se bane hote hain. Classification:
- Saturated (alkanes) — sirf C-C single bonds, e.g. CH4, C2H6
- Unsaturated — alkenes (C=C, e.g. C2H4) aur alkynes (C≡C, e.g. C2H2)
- Aromatic — delocalized ring system, e.g. benzene C6H6
IUPAC naam do: (i) CH3-CH2-CH(CH3)-CH(CH3)-CH2-CH3 (ii) C6H5-CH2-CH3
(i) 6-carbon chain, methyls C3 aur C4 pe → 3,4-dimethylhexane
(ii) Benzene ring pe ethyl substituent → ethylbenzene
Propane preparation ke liye Wurtz reaction likho aur balance karo.
Propane C3H8 (odd carbon) Wurtz se cleanly nahi banta (mixture issue), lekin symmetric hexane C6H14 banta hai:
2 CH3CH2CH2Br + 2Na --dry ether--> CH3CH2CH2-CH2CH2CH3 + 2NaBr
Ethane (C2H6) ka balanced combustion equation likho. 30 g ethane completely jalane par kitne moles CO2 aur H2O banenge?
2C2H6 + 7O2 → 4CO2 + 6H2O
Molar mass C2H6 = 30 g/mol → 30 g = 1 mol
1 mol C2H6 se: CO2 = 1×(4/2) = 2 mol; H2O = 1×(6/2) = 3 mol
But-1-ene geometrical isomerism dikhayega ya nahi? Reason do.
CH2=CH-CH2-CH3 me C1 pe do identical H atoms hain — geometrical isomerism ke liye har doubly-bonded carbon pe do different groups chahiye. Isliye but-1-ene geometrical isomerism nahi dikhata.
Propene + HBr ka product (a) normal condition me (b) peroxide presence me predict karo.
(a) Markovnikov's rule — H us carbon pe jata hai jisme pehle se zyada H hain (secondary carbocation zyada stable):
CH3-CH=CH2 + HBr → CH3-CHBr-CH3 (2-bromopropane)
(b) Peroxide/Kharasch effect (sirf HBr ke liye) — free radical mechanism, Br terminal carbon pe:
CH3-CH=CH2 + HBr --peroxide--> CH3-CH2-CH2Br (1-bromopropane)
Compound B, ozonolysis (Zn/H2O) ke baad sirf ek product deta hai — propanone (acetone). B ka structure aur IUPAC naam do.
Sirf ek identical ketone product milna matlab B symmetrical tetrasubstituted alkene hai:
(CH3)2C=C(CH3)2 --O3/Zn-H2O--> 2 (CH3)2C=O
B = 2,3-dimethylbut-2-ene
Ethyne se benzene banane ki reaction likho.
Cyclic polymerisation (red-hot iron tube, ~873 K):
3 CH≡CH --873 K, Fe tube--> C6H6 (benzene)
Benzene ki resonance/stabilization energy nikalo. Diya hai: cyclohexene hydrogenation ΔH = −120 kJ/mol; benzene hydrogenation (actual) ΔH = −208 kJ/mol.
Theoretical (agar benzene 3 isolated C=C wala cyclohexatriene hota):
3 × (−120) = −360 kJ/mol
Resonance energy = Theoretical − Actual:
−360 − (−208) = −152 kJ/mol
Matlab benzene actual me 152 kJ/mol zyada stable hai delocalization ki wajah se.
Huckel's rule ke basis pe bataiye kaunse aromatic hain: cyclopentadienyl anion (C5H5−), cyclobutadiene, cycloheptatrienyl cation (tropylium, C7H7+).
Huckel's rule: planar, cyclic, fully conjugated, π electrons = 4n+2.
- Cyclopentadienyl anion — 6π (n=1) → aromatic
- Cyclobutadiene — 4π (4n form, n=1) → antiaromatic (aromatic nahi)
- Tropylium cation — 6π (n=1) → aromatic
Benzene + n-propyl chloride/anhyd. AlCl3 (Friedel-Crafts alkylation) ka major product predict karo.
n-Propyl cation (1°, unstable) hydride shift se secondary (2°, zyada stable) isopropyl cation me rearrange ho jata hai. Isliye major product:
Isopropylbenzene (cumene), n-propylbenzene minor product ke roop me.
Toluene ka nitration hone par major products kaunse honge aur kyun?
-CH3 ek o,p-director (activating, +I/hyperconjugation) hai. Isliye major products o-nitrotoluene aur p-nitrotoluene hain (m-nitrotoluene minor); para usually thoda zyada due to less steric hindrance.
Free radical halogenation ki reactivity order F2, Cl2, Br2, I2 me se bataiye aur iodination difficult kyun hai.
Reactivity order: F2 >> Cl2 > Br2 > I2 (bond dissociation enthalpy aur reaction exothermicity ke basis pe). Fluorination itna exothermic hai ki explosive/uncontrollable hota hai. Iodination endothermic aur reversible hai — HI banta hi wapas alkane me react kar leta hai — isliye oxidizing agent (jaise HIO3) chahiye HI hatane ke liye.
Ethane, ethene, ethyne ko kaise distinguish karoge (chemical tests)?
- Ethyne — terminal ≡C-H acidic hai, ammoniacal AgNO3 ke saath white/grey ppt (silver acetylide) deta hai.
- Ethene — bromine water aur Baeyer's reagent (alk. KMnO4) ko turant decolorize karta hai (addition reaction); AgNO3 test negative.
- Ethane — na bromine water decolorize karta hai (dark/cold me), na Baeyer's test positive deta hai — dono negative.
Ek hydrocarbon me sirf C aur H hain — mass % C = 92.3, mass % H = 7.7. Molar mass 78 g/mol hai. Molecular formula nikalo.
100 g compound me moles:
n(C) = 92.3/12 = 7.69; n(H) = 7.7/1 = 7.7
Ratio C:H ≈ 1:1 → empirical formula = CH (mass = 13)
n = 78/13 = 6
Molecular formula = C6H6 → benzene
Ek alkyne C6H10 hot alkaline KMnO4 se oxidise hone par ethanoic acid (CH3COOH) aur butanoic acid (CH3CH2CH2COOH) deta hai. Alkyne ka structure/IUPAC naam do.
Hot KMnO4 internal triple bond ko cleave karke dono taraf -COOH bana deta hai. Fragment carbon count match karo: CH3COOH (2C) + CH3CH2CH2COOH (4C) = 6 carbons total ✓
CH3-C≡C-CH2-CH2-CH3 --hot KMnO4--> CH3COOH + HOOC-CH2-CH2-CH3
Alkyne = hex-2-yne
Alkanes mainly substitution reactions kyun dete hain jabki alkenes/alkynes mainly addition?
Alkanes fully saturated hain — koi π bond nahi jisme electrophile/radical add ho sake; sirf strong C-H/C-C σ bonds hote hain jo radical conditions me homolytically break hote hain → substitution.
Alkenes/alkynes ke π electrons weakly held aur electron-rich hote hain — electrophiles inhe easily attack karte hain aur π bond khulkar naye σ bonds banata hai → addition.
Benzene molecule me kitne sigma aur kitne pi bonds hain?
Benzene C6H6: 6 C-C σ bonds (ring) + 6 C-H σ bonds = 12 sigma bonds. Baaki 3 π bonds pura ring me delocalized hain (kisi ek fixed C-C pe nahi) = 3 pi bonds.
Polynuclear aromatic hydrocarbons (PAHs) health ke liye harmful kyun mane jaate hain? Ek line me explain karo.
Benzo[a]pyrene jaise PAHs coal tar, tobacco smoke aur incomplete combustion (jaise vehicle exhaust) se banate hain aur inme carcinogenic (cancer-causing) properties hoti hain — isliye inka exposure minimize karna zaroori hai.
Important Equations — Ek Nazar Me
| Concept | Formula / Rule |
|---|---|
| Alkanes (general formula) | CnH2n+2 |
| Alkenes / Cycloalkanes | CnH2n |
| Alkynes | CnH2n−2 |
| Degree of Unsaturation (IHD) | (2C+2+N−H)/2 |
| Markovnikov's Rule | Unsymmetrical alkene + HX → H us carbon pe jata hai jisme pehle se zyada H atoms hain (major, zyada stable carbocation route) |
| Peroxide (Kharasch) Effect | Sirf HBr + peroxide → anti-Markovnikov addition (free radical mechanism) |
| Huckel's Rule (Aromaticity) | Planar + cyclic + fully conjugated + π electrons = 4n+2 (n = 0,1,2...) |
| Wurtz Reaction | 2R-X + 2Na --dry ether--> R-R + 2NaX |
| Ozonolysis | C=C bond cleave hota hai; har carbon pe =O aata hai (reductive: Zn/H2O) |
| Combustion (general) | CxHy + O2 → x CO2 + (y/2) H2O |
↔ Table ko side me swipe karein
Common Mistakes — Yahan Marks Kat te Hain
- Markovnikov's rule galat direction me yaad rakhna — H hamesha 'more-H-wale' carbon pe jaata hai, X zyada substituted carbon pe (carbocation stability se), na ki iske ulta.
- Peroxide effect ko HCl ya HI ke saath bhi apply kar dena — anti-Markovnikov addition sirf HBr ke saath hoti hai; HCl aur HI me peroxide effect nahi chalta.
- Benzene ko literal alternate single-double bond structure maan lena aur sigma/pi bond count galat kar dena — 3 π electrons pure ring me delocalized hain, kisi fixed C-C pe nahi.
- Conformers (jaise ethane ke eclipsed/staggered forms) ko structural isomers samajh lena — conformers same compound ke rotational forms hain, alag isomer nahi.
- Wurtz reaction se unsymmetrical alkyl halides mix karke clean single product ki umeed karna — teen products ka mixture banta hai jo separate karna mushkil hai.
- Directive influence me halogens (-Cl, -Br) ko activating maan lena — halogens deactivating hote hain (ring ko electron-poor karte hain) phir bhi o,p-directors hote hain, ye ek exception hai jo saare -EWG=meta rule se bahar hai.
Board-Style Important Questions
- Very short answer: Huckel's rule ka statement likho aur bataiye ye kis type ke molecules pe apply hota hai.
- Short answer: Propene + HBr peroxide presence me react karta hai — mechanism ke saath major product batao.
- Long answer: Ek alkene ozonolysis pe do mole ek hi ketone deta hai jiska molar mass 58 u hai. Alkene ka structure aur IUPAC naam nikalo. (Hint: acetone, (CH3)2CO)
- Long answer: Free radical mechanism se methane ki monochlorination ke steps likho (initiation, propagation, termination).
- Long answer: Benzene ki nitration ka electrophilic substitution mechanism steps me likho, aur samjhao toluene me -CH3 group ortho-para director kyun hai.
Aksar Poochhe Jaane Wale Sawaal
Class 11 Chemistry 2026-27 session me kul kitne chapters hain?
"class 11 chemistry syllabus 2026-27 rationalised" ke hisaab se ab sirf 9 chapters hain (pehle 14 the) — poori "class 11 chemistry all chapters list ncert" ke liye README/syllabus page dekho. Hydrocarbons in 9 me 9th, yaani akhri chapter hai.
Hydrocarbons chapter se board exam me kitne marks aate hain?
Official marks-weightage yahan claim nahi ki ja sakti kyunki wo saal-dar-saal aur board circular se decide hoti hai. Lekin concept-wise ye ek high-yield chapter hai — teen mechanism types (substitution, addition, aromatic substitution) is chapter me hain, isliye reaction-based questions frequently poochhe jaate hain.
Class 11 Chemistry ke saare chapters ki NCERT solutions PDF kahan milegi?
"class 11 chemistry ncert solutions pdf" ke liye official NCERT textbook aur solutions ncert.nic.in (ya NCERT ki official app) se download karo — wahi authoritative source hai. Iss page pe har chapter ke intext/exercise questions ka detailed working diya gaya hai practice ke liye.
Organic Chemistry Basic Principles aur Hydrocarbons chapter ka connection kya hai?
"class 11 chemistry organic chemistry basic principles and techniques notes" me jo IUPAC nomenclature, isomerism aur electronic effects (inductive, resonance) padhaye jaate hain, Hydrocarbons chapter unhi concepts ko real molecules (alkanes, alkenes, alkynes, benzene) pe apply karta hai — dono chapters saath revise karna best hai.
Class 11 Chemistry me kaunse topics is session me deleted hain?
"class 11 chemistry deleted syllabus topics" me States of Matter (Gases and Liquids), Hydrogen, s-Block Elements, Some p-Block Elements aur Environmental Chemistry shamil hain — ye 5 poore chapters/units rationalise karke hata diye gaye hain, is session me nahi padhaye jaate.
Baaki Class 11 Chemistry chapters (Structure of Atom, Equilibrium, Redox, Chemical Bonding) ke notes/important questions kahan milenge?
Agar "class 11 chemistry chapter 2 structure of atom important questions" ya "structure of atom class 11 formulas" chahiye, ya "some basic concepts of chemistry class 11 notes", "classification of elements and periodicity in properties important questions", "chemical bonding and molecular structure class 11 notes pdf", "class 11 chemistry chapter 5 thermodynamics numericals", "redox reactions class 11 important questions", ya "class 11 chemistry chapter 6 equilibrium ncert solutions" — ye sab chapters isi tarah ke dedicated solution pages me cover kiye jaate hain, is Hydrocarbons page ke saath series me dekho.
Class 11 Chemistry — Saare Chapters
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