JEE NEET Chemistry Question Bank - Hydrocarbons

21 Hydrocarbons
ˆ Classification of Hydrocarbons
Simple organic compounds having only carbon and hydrogen are called hydrocarbons. Their is clas-
sification as follows :

Hydro carbon Type Charac- General Bond Example
teristic formula

Alkane acyclic saturated CnH2n + 2 C – C CH3 – CH2 – CH3 propane
cyclic saturated CnH2n C – C CH2 cyclo propane

H2C CH2

alkene acyclic unsaturated CnH2n C = C CH3 – CH = CH2 propene

cyclic unsaturated CnH2n – 2 C = C CH2 cyclo propene

HC CH

alkyne acyclic unsaturated CnH2n – 2 C º C CH3 – C º CH propyne

arene cyclic specific CnH2n – 6m alternate

unsaturation C – C and Benzene
C = C
• Classification of carbon atoms in hydrocarbon
(i) Carbon connected with one other carbon is called primary (1o) carbon.

(ii) Carbon connected with two other carbon is called secondary (2o) carbon.

(iii) Carbon connected with three other carbon is called tertiary (3o) carbon.

(iv) Carbon connected with four other carbon is called quaternary (4o) carbon.

1. Which of the following is a saturated hydrocarbon ?

(A) Propene (B) Benzene (C) Cyclohexane (D) Acetylene

2. Which of the following is isomer of cyclo alkene ?
(A) cyclo alkane (B) alkyne (C) alkene (D) arene
3. What is the general formula of cyclic alkene ?

(A) CnH2n+2 (B) CnH2n-2 (C) CnH2n (D) CnH2n+1

4. Which of the following substance contains tertiary carbon ?
(A) Propane (B) n – butane (C) 2 – Methyl propane(D) Methane
490

5. Which of the following compound is only acyclic ?
(A) alkane (B) alkene (C) alkyne (D) arene
6. Which hydro carbon has 4o carbon ?
(A) isobutane (B) n–hexane (C) neopentane (D) n–butane
7. In which of the following hydro carbon compound all four types of carbon (1o, 2o, 3o, 4o) are
present ?
(A) 2, 3–dimethyl butane (B) 2, 2 dimethyl butane
(C) neo pentane (D) 2, 2, 3 trimethyl pentane
8. How many tertiary carbon atoms are present in 2, 3 dimethyl butane ?
(A) 1 (B) 2 (C) 3 (D) 4
9. Number of 1o, 2o, and 3o hydrogen atoms present in neopentane are ...... respectively.
(A) 0, 12, 6 (B) 12, 2, 0 (C) 6, 2, 0 (D) 12, 1, 1
10. ...... is example of alkyne.
(A) C5H8 (B) C8H16 (C) C9H18 (D) C7H16

Answers : 1. (C), 2. (B), 3. (B), 4. (C), 5. (C), 6. (C), 7. (D), 8. (B), 9. (B), 10. (A)

ˆ General information, Nomenclature and isomerism in alkane
ˆ General Information :
® sp hybridization and tetrahedral shape.
3

® C – C and C – H bond length 154 and 112 pm.respectively
® H – C – H bond angle 109 28' o

® Nomenclature : Refer Unit : 20
® Isomerism :
In alkane chain isomerism and conformational isomerism is observed. Out of which chain
isomerism is discussed in unit 20.
Conformational isomerism : In alkane C – C single bond can rotate along with its bond
axis. As a result hydrogen or atoms connected with both carbon can arranged at different distance
and various spatial arrangement become possible. These are known as conformer isomers or
rotamers. Out of these two isomers staggerd and eclipsed are important other isomers are in
between two out of which skew or gauche is also important onc.
Two conformer of ethane are as follows :
Newmann projection Sawhorse projection

H H
H H
H H H H H
H
H
H H
H
H H H H H H H
H H H

Staggered Eclipsed Staggered Eclipsed
491

ˆ In staggered structure hydrogen of both carbon are arranged far from each other hence repulsion
is less so it is more stable. (dihedral angle 180°)
ˆ In eclipsed structure hydrogen of both carbon are arranged closer (in diff plane) from each other
hence, repulsion is more so stability is less (dihedral angle 0°)
ˆ Out of staggered and eclipsed, staggered is more stable.
ˆ Stability order for conformers of butane is as follows :
Staggered (anti) > Skew or Gauche > Partially eclipsed > Fully eclipsed
ˆ In cyclohexane chair and boat conformers are observed out of which chair conformer is more
stable.

11. In alkane compound C – H bond length and, H – C – H bond angle is ...... respectively.
(A) 112 pm 120o (B) 112 pm, 109o 281 (C) 154 pm, 109o 281 (D) 135 pm, 180o
12. Which of the following is the structure of isobutyl group ?
(A) CH3 – CH2 – CH2 – CH2 – (B) CH3 – CH – CH2 –

CH3
(C) CH3 – CH – CH2 – CH3 (D) (CH3)3 – C –

13. Which sentence is incorrect with reference to isopentane ?
(A) It has three methyl group. (B) It has only one – CH2 group.
(C) It has one – CH group . (D) It has one quaternary carbon

14. Which of the following compound has isopropyl group ?
(A) 3, 3–dimethyl pentane (B) 2, 2, 3, 3–tetramethyl pentane
(C) 2–methyl pentane (D) 2, 2, 3–tri methyl pentane
15. Acidic saturated hydrocarbon has molor mass 72 gm/mol then how many isomers are possible for
it ?
(A) 2 (B) 4 (C) 5 (D) 3
16. C – H bond length is least in ......
(A) C2H2 (B) C2H4 (C) C2H6 (D) C2H2Br2
17. Which of the following is staggered conformer of ethane ?

H
H
H H
H
(A) (B) H
H
H H
H
H H

H
H

(C) (D) None of the three.
H
H H
H

492

18. Out of four conformer of n–butane which one is most stable ?
(A) eclipsed (B) partially eclipsed (C) staggered (D) gauch

19. Which structure of cyclo hexa triene is most stable ?

(A) chair (B) boat (C) half chair (D) plannar

20. In which of the following cyclic structure maximum strain is observed ?

(A) Cyclohexane (B) Cyclo pentane (C) Cyclo butane (D) Cyclo propane

Answers : 11. (B), 12. (B), 13. (D), 14. (C), 15. (D), 16. (C), 17. (A), 18. (C), 19. (D), 20. (D)

ˆ Preparation and properties of alkane
ˆ Preparation :

By hydrogenation of alkene and alkyne

Pt / Pd
R – CH = CH2 + H2 R – CH2 – CH3

Pt / Pd
R – C ≡ CH + 2H2 R – CH2 – CH3 (R = alkyl group)
ˆ Reduction of alkyl halide
Zn / HCl
R – X + H2 R – H + HX

ˆ By decarboxylation of sodium salt of carboxylic acid

Soda lime
R – COONa R – H + Na2CO3
NaOH + CaO

ˆ Wurtz reaction

dry
2R – X + 2Na ether R – R + 2 NaX

ˆ Grignard reaction

dry
ether HX
R – X + Mg R – Mg – X R – H + Mg X2

ˆ Frankland reaction

dry
2R – I + Zn ether R – R + ZnI2

ˆ By reduction of carbocyclic acid, aldehyde ketone and alcohol alkane is formed.
ˆ Correy-house reaction

R - X + R ’2CuLi 
→ R - R’ + RCu + LiX (R and R' same or different)

493

ˆ Kolbe’s electrolytic method

electrolysis
2 R – COONa + 2H2O R – R + 2CO2+ 2NaOH + H2

at anode at cathode
ˆ Physical properties
ˆ Alkane having C1 to C4 are gaseous, C5 to C17 are liquid C18 or more than C18 are solids.

ˆ In alkane series or number of carbon increases boiling point increases.

ˆ As alkane is nonpolar insoluble in water but in non polar solvent like benzene it is soluble.

ˆ In alkane boiling point decreases from 1o ®2 ®3. o o

ˆ Chemical properties
ˆ Halogenation : Reactivity order F2 > Cl2 > Br2 > I2.

hv
CH4 + Cl2 CH3 – Cl + HCl

Ni
ˆ Reaction with steam : CH4(g) + H2O(g) CO(g) + H2(g)

water gas

ˆ Arromatization :

Mo2O3 or V2 O5 or Cr2 O3
CH3 – (CH2)4 – CH3 + 4H2
773K, 10–20 bar

n-hexane benzene

ˆ Isomerization :

Anhy
[AlCl 3]
CH3 – CH2 – CH2 – CH3 CH3 – CH – CH3 ..... isobutane

n-butane CH3

ˆ Racking :
770–970K
2CH3CH2CH3 CH3 – CH = CH2 + CH2 = CH2 + CH4 + H2
propane propene ethene Methane
ˆ Nitration : CH4 + HNO3 
→ CH3NO2 + H2O
Methane Nitro methane
675 K
ˆ Sulphonation : C6H14 + H2SO4 C6H13 – SO3H + H2O
hexane hexane sulphonic acid

ˆ Oxidation : CH4(g) + 2O2(g) CO2(g) + 2H2O(g) + heat

494

21. Conversion of but–1–ene into but-2-ene is done by reacting it with .......
(A) Pd / H2 (B) Zn / HCl (C) Sn / HCl (D) Zn – Hg

22. By which method propane can be obtained form propene ?
(A) Wurtz reaction (B) Grignard reaction
(C) Catalytic hydrogenation (D) Frank land reaction
23. In preparation of propane from propyne hybridization of carbon changes from ......
(A) sp2 to sp (B) sp2 to sp3 (C) sp to sp3 (D) sp3 to sp
24. By which reaction butane can be prepared from ethyl chloride in one step ?
(A) Wurtz reaction (B) Frankland reaction (C) Hydrogenation (D) Grignard reaction
25. Preparation of methane can be done by ......
(A) hydrogenation (B) water reaction (C) decarboxcylation (D) all the given
26. By which method alkene having same no of carbon can be prepared from halo alkane ?
(A) Wurtz reaction (B) Grignard reaction (C) reduction (D) both (B) and (C)
27. Kolbe’s electrolysis of sodium acetate gives ...... .
(A) methane (B) ethane (C) ethene (D) acetic acid
28. ...... has highest boiling point.
(A) n-hexane (B) n-pentane
(C) 2-methyl butane (D) 2, 2-dimethyl propane
29. Boiling point of neopentane is more than ...... .
(A) iso pentane (B) n-pentane (C) butane (D) n-hexane
30. Benzene obtained from n-hexane by ...... reaction.
(A) isomerism (B) Craking (C) rearrangement (D) cydization
31. Kerosene is a mixture of ...... .
(A) alkanes (B) aromatic compounds (C) alcohols (D) CO + H2
32. Which compound gives methane by reaction with water ?
(A) Al4C3 (B) CaC2 (C) VC (D) SiC

33. For following conversion CH3CH2COOH 
→ CH3CH2CH3 which reagnet is appropriate ?

(A) LiAlH4 (B) Sodalime (C) Red P / HI (D) Zn / HCl
34. Halogenation of alkane is example of which of the following ?
(A) Electrophilic substituion (B) Nuclcophilic substitution
(C) Free radical substitution (D) addition reaction
35. Which parafin is solid at room temperature ?
(A) C3H8 (B) C8H18 (C) C4H10 (D) C20H42

Answers : 21. (A), 22. (C), 23. (C), 24. (A), 25. (C), 26. (D), 27. (B), 28. (A), 29. (C),
30. (D), 31. (A), 32. (A), 33. (C), 34. (C), 35. (D)

495

ˆ General information, Nomenclature and isomerism of alkene
ˆ sp2 hybridization and trigonal plannar shape

ˆ C – C and C – H bond length 134 and 110 pm respectively

ˆ H – C – H bond angle 116o6’ and C – C – H bond angle 121o7’

ˆ Nomenclature : Refer Unit : 20

ˆ Isomerism : Alkene has position isomerism, chain isomerism and geometrical isomerism
position isomerism is discussed in unit 20.

ˆ Geometrical isomerism : In some alkene compounds though their molecular and structural
formula are same but atoms or groups arranged differently in space in different direction.
Which is called geometrical isomerism. Geometrical isomers shown by cis and trans.

ˆ This isomerism is observed in planner molecule having C = C.

ˆ Due to restricted rotation around C = C geometrical isomerism arises.

ˆ Two isomers of but–2–ene are as follows :

CH3 CH3 CH3 H
C=C or C=C
H H H CH3

cis but-2-ene trans but-2-ene

ˆ Geometrical isomerism is observed in compounds like ab C = C ab, ab C = C ad ab C = C
de but it is not observed in the compounds like ab C = C bb or aa C = Cab type of
compounds.

ˆ cis isomer is polar while trans isomer is non-polar.

ˆ cis isomer has greater solubilly in water than trans isomer.

36. In ethene C = C and C – H bond length is ...... respectively.
(A) 134, 112 (B) 154, 112 (C) 134, 110 (D) 139, 110

37. Shape of ethene molecule is ...... .
(A) linear (B) tetrahedral (C) octahedral (D) trigonal plannar
38. IUPAC name of (CH3)2 . CH – CH = CH – CH = CH is ...... .

CH – CH3

C2H5
(A) 2, 7–dimethyl nona 3, 5–diene (B) 2, 7–dimethyl octa–3, 5–diene
(C) 2–ethyl 7–methyl octa–3, 5–diene (D) 7–methyl non–3–ene

496

39. IUPAC name of is ......

(A) 4–ethyl 3–methyl pent–4–en–1–yne (B) 2–ethyl 4–methyl pent–1–en– 4–yne
(C) 4–ethyl 3–Methyl pent–1–yne–4–ene (D) 2–ethyl 3–methyl pent–4–yne–1–ene

40. Which compound shows geometrical isomerism ?
(A) butane (B) but–1–ene (C) but–2–ene (D) but–2–yne

41. Number of possible alkene isomers of C4H8 is ...... .
(A) 2 (B) 3 (C) 4 (D) 5

42. In which of the following compound carbon has sp and sp2 hybridization.
(A) propene (B) propyne
(C) propadiene (D) none

43. Hybridization of carbon atoms buta 1, 3–diene is ...... type.
(A) sp, sp2, sp3 (B) sp2, sp3 (C) sp, sp2 (D) Võík sp2

44. How many alkene isomers of C5H10 are possible ?
(A) 7 (B) 5 (C) 4 (D) 6

45. Number of isomers of C2H2Br2 is ...... .
(A) 1 (B) 2 (C) 3 (D) 0
Answers : 36. (C), 37. (D), 38. (A), 39. (B), 40. (C), 41. (C), 42. (C), 43. (D), 44. (D),
45. (C)

ˆ Preparation and properties of alkene
(I) Preparation :

H2
ˆ Hydrogenation of alkyne : R – C ≡ CH R – CH = CH2
Pd / C
Lindler’s catalyst
ˆ Dehydrohalogenation of alkylholide (b – elimination reaction) :

Ethanol
b
CH3 – CH2 – Cl + KOH
a
CH2 = CH2 + KCl + H2O
ˆ From vicinal dihalide :

Br – CH2 – CH2 – Br + Zn CH2 = CH2 + Zn Br2
ˆ Dehydration of alcohol :

concH2SO4
CH3 CH2 OH CH2 = CH2 + H2O
443 K

497

ˆ Kolbe’s electrolysis method :
CH2 – COOK CH2
electolysis
+ 2H2O + 2CO2 + 2 KOH + H2
CH2 – COOK CH2
at anode at cathode
(II) Physical properties :
ˆ Boiling point of alkyne is more than corresponding alkane due to polar nature.
ˆ Boilling point of cis isomer is more than trans isomer.
ˆ Melting point of trans alkene is more than cis isomer.
ˆ In soluble in water but soluble in organic solvent.
ˆ In isomers boiling point decreases from 1o ® 2o ® 3o.
(III) Chemical Properties :
Due to p–bond alkene shows following additional reactions :

Pt / Pd
ˆ Hydrogenation : CH2 = CH2 + H2 CH3 – CH3

ˆ Halogenation : CH2 = CH2 + X2 
→ X – CH2 – CH2 – X where, X = Cl, Br, I

ˆ Hydrohalogenation :

(a) Symmetric alkene CH2 = CH2 + HX 
→ CH3 – CH2 – X (X = Cl, Br, I)

(b) Asymmetric alkene : CH3 – CH = CH2 + HX 
→ CH3 – CH – CH3 2–halo propane

X
Note : Hydrohalogenation of asymmetric alkene follows Markovnikoff rule : As per this rule
negative part of reagent. Combine with ethylenic carbon having less number of hydrogen.
(c) Reaction of asymmetric alkene with HBr in presence of peroxide catalyst follows anti

( )
Markovnikoff rule. In this reaction negative part of reagent X combines with ethylenic
carbon having more number of hydrogen.
benzoyl peroxide
eg., CH3 – CH = CH2 + HBr CH3 – CH2 – CH2 – Br
1 – Bromo propane
ˆ This reaction do not take place with HCl or HI.

dilH2SO4
ˆ Hydration : CH2 = CH2 + H2O CH3 – CH2 – OH

dilH2SO4
CH3 – CH = CH2 + H2O CH3 – CH – CH3 (Markovnikoff)

OH
Cold
ˆ Oxidation : (a) CH2 = CH2 CH2 – CH2
alk. KMnO4
OH OH
ethylene glycol
498

During this reaction pink colour of KMnO4 disappear it is known as Bayer’s test for unsaturation.

Hot
(b) CH2 = CH2 2 HCOOH
alk. KMnO4
Formic acid
ˆ Ozonolysis :

O
Zn
R – CH = CH2 + O3 
→ R – CH CH2 R – CHO + HCHO
H2O
O O
Ozonide

46. Which major product is obtained on reaction of chloro ethene with alcoholic KOH ?
(A) ehtane (B) ethene (C) ethanol (D) ethyne
alcoholic
47. CH3 – CH – CH2 – CH3 major product.
KOH
Br
(A) butane (B) but–1–ene (C) but–2–ene (D) butyne
48. Lindlar’s catalyst is mixture of what ?
(A) Ni + H2 (B) Pt / H2 (C) Pd + Pt (D) Pd + charlcol
49. Which substance can form alkene by elimination reaction ?
(A) haloalkane (B) dihaloalkane (C) alcohol (D) all
50. Which compound on heating with Zn gives but-2-ene ?
(A) 2, 3–dibromobutane (B) 1, 2–dibromobutane
(C) but–2–yne (D) None
51. ...... is the gas which removes colour of basic KMnO4 produced by reaction between ethyl
iodidc and alcoholic KOH.
(A) C2H6 (B) C2H4 (C) C2H2 (D) CH4
52. Preparation of alkene from vicinal dihalide known as ...... .
(A) decarboxylation (B) dehydrohelogenation(C) dehalogenation (D) dehydrogenation

CH3
H2SO4
53. Product of CH3 – C – CH3 is.

OH
(A) propene (B) but – 1 – ene (C) propanol (D) 2–methyl propene
54. CH3 – CH2 – CH = CH2 + HBr 
→ .........
(A) CH3 – CH2 – CH2 – CH3 (B) CH3 – CH2 – CH2 – CH2 – Br

(C) CH3 – CH2 – CH – CH3 (D) CH3 – CH2 – C ≡ CH

Br

499

55. CH2 = CH – Cl + HCl 
→ .........
(A) CH3 – CH2 – Cl (B) CH3 – CHCl2 (C) CH2 – CH2 (D) CH ≡ CH

Cl Cl
56. ...... product is obtained on reaction between 2-methyl prop-1-ene and HBr in presence of benzoyl
peroxide.

Br

(A) CH3 – CH – CH2Br (B) CH3 – C – CH3

CH3 3 CH3

(C) CH3CH2CH2CH2Br (D) CH3 – CH2 – CH – CH3

Br
57. For the reaction of which of the following compounds Markonikoff rule is useful ?
(A) C2H4 + HCl (B) C3H6 + Br2
(C) C3H6 + HBr (D) C2H4 + I2
58. R – CH2 – CH = CH2 + ICl 
→
(A) R – CH2 – CH – CH2 – I (B) R – CH2 – CH – CH2 – CI

Cl I
(C) R – CH2 – CH = CH2 (D) R – CH = CH – CH2 – I

I
59. In presence of peroxide alkene do not give anti Markovnikoff reaction with HCl or HI
because ......
(A) both are highly ionic.
(B) one is oxidising agent other is reducing agent.
(C) In both case one step is endothermic.
(D) In both case all the steps are endothermic.
60. Major product of reaction between 3–phenyl propene with HBr is ...... .
(A) C6H5CH2CH(Br)CH3 (B) C6H5CH(Br)CH2CH3
(C) C6H5CH2CH2CH2Br (D) C6H5CH(Br)CH = CH2
61. Which of the following compound do not give reaction with HBr according to Markovnikoff
rule.
(A) Propene (B) but–1–ene (C) but–2–ene (D) pent–2–ene
(C6H 5CO)2O 2
62. isobutene + HBr ...... .
(A) 3o butyl bromide (B) isobutyl bromide
o
(C) 3 butyl alcohol (D) isobutyl alcohol
63. Butene from butane can be formed by reaction with ......
(A) Zn – HCl (B) Sn – HCl (C) Zn – Hg (D) Pd / H2
500

64. Propene on reaction with HI gives isopropyl iodide not n-propyl iodide because ......
(A) Reaction takes place by more stable carbonium ion.
(B) Reaction takes place by more stable free radical.
(C) Reaction takes place by more stable carbonium ion.
(D) none of the above.

65. Identify B in the following reaction sequence :

O3 Zn
CH3 – CH = CH – CH3 A B
H2O

(A) 2CH3CHO (B) 2CH 3COCH 3 (C) 2CH 3COOH (D) CH3CH2CH2CH3

Answers : 46. (B), 47. (C), 48. (D), 49. (D), 50. (A), 51. (B), 52. (C), 53. (D), 54. (C),
55. (B), 56. (A), 57. (C), 58. (A), 59. (C), 60. (B), 61. (C), 62. (B), 63. (D),
64. (A), 65. (A)

ˆ General Information, Nomenclature and isomerism of alkyne
ˆ General information : sp hybridization and linear shape.

ˆ C ≡ C and C – H bond length 120 and 106 pm respectively.

ˆ Bond angle 180o

ˆ Nomenclature : Refer Unit : 20

ˆ Isomerism : In alkyne position, chain and ring chain isomerism is observed.

66. Compound with which of the following bound is most reactive ?
(A) C – C (B) C = C (C) C ≡ C (D) All
67. In which of the following compound all atoms are linearly bonded ?
(A) Propane (B) Propene (C) Propyne (D) All
68. Hybridization of second carbon in buta 1, 2–diene is ...... .
(A) sp (B) sp2 (C) sp3 (D) dsp 2
69. Triple bond between two carbon in alkyne is formed by ...... .
(A) 1 sigma 2 pi (B) 1 pi 2 sigma (C) 3 sigma (D) 3 pi
70. IUPAC name of (CH3)3 C – C ≡ C – C (CH3)3 is ...... .
(A) 3, 3, 4, 4–tetra methyl Hex–3–yne (B) 2, 2, 5, 5–tetra methyl Hex–3–yne
(C) 2, 2, 5, 5–tetra methyl Hex–4–yne (D) di(trimethyl)–2–yne
71. How many alkyne isomers are possible for compound having molecular formula C5H8 ?
(A) 2 (B) 4 (C) 3 (D) 5
72. Which of the following is isomer of propyne ?
(A) Cyclo propyne (B) Cyclo propene (C) Propene (D) Propane
Answers : 66. (C), 67. (C), 68. (A), 69. (A), 70. (B), 71. (C), 72. (B)
501

ˆ Preparation and properties of alkyne
ˆ Preparation :
Hydrolysis of Calcium Carbide :
CaC2 + 2H2O 
→ Ca(OH)2 + CH ≡ CH
Dehydrohalogenation of vicinal dihalide :

ethanol NaNH2
CH2 – CH2 + KOH CH2 = CH CH ≡ CH
– KBr – NaBr
– H 2O – NH3
Br Br Br
Dehalogenation of tetrahalide :

R – C Br2 – CH Br2 + 2Zn R – C ≡ CH + 2ZnBr2
Kolbe’s electrolysis method :
H – C – COOK CH
electrolysis
+ 2H2O + 2CO2 + 2KOH + H2
H – C – COOK CH
potassium malate at anode at cathode
Higher alkyne from acetylene :
Na/Liq . NH3 R–X
CH ≡ CH HC ≡ C– – Na+ R – C ≡ CH + NaX
ˆ Physical properties
ˆ Alkyne is weakly polar.
ˆ Insoluble in water but soluble in non polar solvent.
ˆ Compared to corresponding alkane and alkene, alkynes have higher boiling point and melting point.
ˆ Ethyne and terminal alkyne shows acidic character. They are weak acids.
ˆ Chemical properties
Like alkene alkyne also gives addition reactions. :
ˆ Hydrogenation :

Pd / C H2
ˆ CH ≡ CH + H2 CH2 = CH2 CH3 – CH3
Pd / C
R R
Lindlar’s catalyst
C=C
H2, Pd / C
H H
• R – C ≡ C – R cis – alkene
R H
Birch reduction
C=C
H2, Na/Liq⋅NH3
H R
trans-alkene
502

Halogenation :
Cl2
CH ≡ CH + Cl2 → CHCl = CHCl CHCl2 – CHCl2
Hydrohalogenation :
HB r
CH ≡ CH + HBr → CH2 = CHBr CH3 – CHBr2 (Markovnikoff)
Hydration :
dilH2SO4 re-arrangement
CH ≡ CH + H2O CH2 = CH CH3 – C – H
HgSO4
333K
OH O
Polymerization :

Red hot Fe tube
3CH ≡ CH
775 K
Oxidation :
Cold
(a) CH3 – C ≡ CH CH3COOH + CO2

terminal alkyne
Cold
(a) CH3 – C ≡ C – CH3 CH3 – C – C – CH3

O O
non terminal alkyne
Hot
(b) CH3 – C ≡ CH CH3COOH + CO2

terminal alkyne
Hot
CH3 – C ≡ C – CH3 CH3COOH + CH3COOH

non-terminal alkyne
Ozonolysis :

O
CH CH Zn / H 2O
CH ≡ CH + O3 
→ H – C – C – H
O O
O O
Glyoxal
Acidic nature :
(i) Acetylene and terminal alkynes reacts with strong base like sodamide due to acidic nature.
CH ≡ CH + NaNH2 
→ HC ≡ C– · Na + + NH3
Sodium acetylide
(ii) By decomposing Grignard reagent gives alkane
CH ≡ CH + R – Mg – X 
→ R – H + HC ≡ C – MgX
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73. Colourless gas obtained by reaction between metal carbide and water is ...... .
(A) Methane (B) ethane (C) acetylene (D) ethylene
74. Identify X and Y in the following reaction :

dilH2SO4
CaC2(S) + H2O(1) → X
HgSO4
Y

(A) X–ethylene Y-acetaldehyde (B) X–acetylene Y–ethanol
(C) X–ethane Y–ethanol (D) X–acetylene Y–ethenol
75. 1, 2–di bromo ehtane on reaction with alcoholic KOH gives ...... .
(A) ethane (B) acetylene (C) ethylene (D) methane
76. Product obtain by reaction between haloalkene and sodamide is ...... .
(A) alkane (B) alkene (C) alkyne (D) holo alkane
77. Which of the following compound has acidic hydrogen ?
(A) ethene (B) ethyne (C) propyne (D) both (B) and (C)
78. By which of the following reaction propyne is formed ?
(A) CH3Br with acetylene (B) CH3Br with sodium acetylide
(C) CH3I with sodium acetate (D) Methane with ethene
79. Oxidation of but-1-yne by hot alkaline KMnO4 gives ...... .
(A) CH3CH2CH2COOH (B) CH3CH2COOH
(C) CH3CH2COOH + CO2 + H2O (D) CH3CH2COOH + HCOOH
80. ...... is obtained by reaction between acetylene and ethyl magnesium bromide.
(A) Butane (B) Ethane (C) but-1-ene (D) but–2–ene
81. Final product of reductive ozonolysis of but–2–yne is ...... .
(A) glyoxal (B) 2CH 3COOH (C) but 2, 3 – dione (D) butanal
82. Final product of C2H2 with HCl is ......

(A) CH = CH – Cl (B) CH3 – CHCl2 (C) CH – Cl (D) None

CH – Cl
HgCl2
83. CH ≡ CH + HCl product.
(A) Methyl chloride (B) Dichloro ethane (C) Vinyl chloride (D) Ethyl chloride
84. Which final product is obtained by reaction of propyne with dilute H2SO4 in presence of
HgSO4.
(A) propanal (B) propyl hydrogen sulphate
(C) propanal (D) acetone
85. ...... type of reactions are given by alkyne compounds.
(A) substitution (B) addition (C) polymerization (D) all
Answers : 73. (C), 74. (D), 75. (B), 76. (C), 77. (D), 78. (B), 79. (C), 80. (B), 81. (C),
82. (B), 83. (C), 84. (D), 85. (D)
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ˆ Arene (aromatic hydro carbon) General information, Nomencluture and structure of benzene
ˆ Compounds having benzene ring are called aromatic compounds.
ˆ Aromatic compounds having only carbon and hydrogen are called aromatic hydrocarbon or arene.
Their first member is benzene.
ˆ General formula of arene is CnH2n – 6m where m = number of rings
ˆ Aromatic compounds having benzene ring are called benzanoids. eg. biphenyl, napthalene,
anthracene, phenanthrene, napthacene
ˆ Aromatic compounds which do not have benezene ring are called non-benzaoids. eg. pyrol, furan,
thiofin, pyridine.
ˆ Nomencluture
ˆ By displacing hydrogen of benzene with other group substituted benzene can be obtained.

CH3 NO2 CH3 CH3 CH3
CH3

CH3
CH3
benzene methyl nitro benzene o– xylene m –xylene p– xylene
benzene (Toluene)

ˆ Structure of Benzene
ˆ Molecular formula of benzene is C6H6. It has hexagonal cyclic structure with alternate C – C and
C = C.
ˆ Resonating structure of benzene as per kekule is as follows :

ˆ Mono substituted benzene has only one isomer while disubstituted has three isomers (or the
meta and para)
ˆ Benzene has less chemical reactivity and greater stability is called aromatic character.

ˆ Benzene follows (4n + 2) pe– rule of Huckel hence it is aromatic.

86. Which of the following is aromatic hydrocarbon ?
(A) cyclohexane (B) toluene (C) phenol (D) aniline
87. Molecular formula of anthracene is ...... .

(A) C6H6 (B) C6H12 (C) C10H8 (D) C14H10
88. Which of the following is non benzanoid ?
(A) Napthalene (B) Aniline (C) Pyridine (D) Napthacene

89. Reaction of benzene with 3 moles Cl2 in presence of sunlight gives ...... product.

(A) C6H3Cl3 (B) C6Cl6 (C) C6H6Cl6 (D) C6H5Cl
90. Chemical name of pesticide gamaxene is ...... .
(A) DDT (B) BHC (C) chloral (D) hexa chlorethane
505

91. Carbon-carbon bond length in benzene is ...... pm.
(A) 154 and 134 (B) only 134 (C) only 154 (D) 139
92. Which product is obtained by ozonolysis of benzene followed by hydorlysis of product ?
(A) Benzenetriozonide (B) acetaldehyde (C) glyoxal (D) benzone
93. According to Huckel’s rule how many pe–s are present in phenanthrene ?
(A) 6 (B) 10 (C) 12 (D) 14
94. Benzene shows ...... type of reaction.
(A) substitution (B) addition (C) oxidation (D) all the given
95. How many s and p bonds are present in biphenyl respectively ?
(A) 22 and 6 (B) 23 and 6 (C) 13 and 5 (D) 12 and 6
96. Which of the following sentence is correct for benzene ?
(A) Due to unsaturation benzen gives addition reaction easily.
(B) In benzen 3 types of C–H bond.
(C) In benzene cyclic delocalized p bonds are present.
(D) In benzene 6p electrons are localized.
97. Number of s and p bonds in phenol are ...... respectively.
(A) 13, 2 (B) 12, 3 (C) 13, 3 (D) 13, 4
98. What is the hybridization of all six carbon in benzene ?
(A) sp (B) sp2 (C) sp3 (D) sp2 and sp3
99. Why benzene has higher stability and less reactivity ?
(A) sp3 hybridization of six carbon atom (B) cyclic structure of six carbon atom
(C) high resonance energy (D) unsaturated nature of benzene ring
100. Which compound do not follow Huckel’s rule ?
(A) Benzene (B) Cyclohexane (C) Napthalene (D) Pyrol

Answers : 86. (B), 87. (D), 88. (C), 89. (C), 90. (B), 91. (D), 92. (C), 93. (D), 94. (D),
95. (B), 96. (C), 97. (C), 98. (B), 99. (C), 100. (B)

ˆ Preparation of Benzene
ˆ By cyclic polymerization of ethyne

red hot Fe tube
3CH ≡ CH
873 K
ˆ By decarboxylation of sodium benzoate

COONa
sodalime
+ Na2CO3
NaOH + CaO

ˆ By reduction of phenol
506

OH
Zn
+ ZnO

ˆ Electrophillic substitution reaction of benzene
NO2
Nitration
+ H2 O
conc. HNO 3+ conc. HSO4
323–333 K nitrobenzene

SOH
3
Sulphonation
+ H2 O
conc. H2SO4 + SO 3
353 K benzene sulphonic acid
Cl
Chlorination
+ Hl
Cl2
[Fe Cl3] 303–313 K chlorobenzene
Br
Benzene Bromination
+ Hr
Br2
[Fe Br3] Bromobenzene
CH
Friedel Craft acylation
+ HlC
CHCl
[Any.AlCl 3] 353 K Toluene
COCH
Friedel Craft acylation
+ HlC or CHCOOH
CH3COCl (CH3CO)2O
[Anhy.AlCl3] 353 K Acetophenone

ˆ Directive effect of inductive group
ˆ Due to effect of first group connected with benzene, at which position second group is
connected is determined. Hence 1st group present in mono substituted benzene is called inductive
group and this effect is called directive effect.

ˆ Directive effect are at two types :

(a) o and p directive group (e– donor group)

–R, –C6H5, –X, –OH, – OR, –NH2, –NHR, –NR2, –NHCOR

(b) meta directive group (e– attracting group)

–NO2, –SO3H, –COOH, –COOR, –CN, –CHO, –COR, –CCl3
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101. By which reaction of phenol, benzene can be obtained ?
(A) oxidation (B) reduction (C) decarboxilation (D) cyclization

102. Which of the following is strongest o/p directive group ?

(A) –OH (B) –Cl (C) –C6H 5 (D) –Br

103. due to inductive effect of which group in benzene substitution takes place at meta position ?

(A) –NH 2 (B) –Cl (C) –CH 3 (D) –COCH 3

104. Which of the following compound produces meta product during chlorination?

(A) ethoxy benzene (B) chloro benzene (C) ethyl benzoate (D) toluene

105. Electrophilic ion substituted during acylation of benzene is ...... .

(A) +CH3 (B) CH 3– (C) +SO3H (D) CH3+CO

106. Product obtained by nitration of benzene is ...... (Temperature 323 K)

(A) nitro benzene (B) nitroso benzene

(C) O-dinitro benzene (D) m–dinitrobenzene

107. Product obtained by reaction of benzene with concentrated HNO3 and H2SO4 of 353 to
363 K temperature is ...... .

(A) benzene sulphonic acid (B) nitro benzene

(C) m–dinitro benzene (D) (o and p) dinitro benzene

108. Which of the following compound is most reactive towards electrophilic aromatic substitution
reaction ?

(A) benzene (B) toluene (C) benzoic acid (D) nitro benzene

109. In which of the following compound second substituion is difficult ?

(A) toluene (B) chloro benzene (C) phenol (D) aceto phenone

110. At which position new group will enter during nitration of toluene ?

(A) ortho (B) meta (C) para (D) ortho + para

Answers : 101. (B), 102. (A), 103. (D), 104. (C), 105. (D), 106. (A), 107. (C), 108. (B),
109. (D), 110. (D)

ˆ Reaction and conversion of toluene
Reaction of phenyl group in toluene :
ˆ Toluene also gives electrophillic substitution reaction like benzene for eg. nitration, sulphonation,
chlorination, bromination, alkylation, acylation etc.
ˆ – CH3 group in toluene is ortho-para directive group hence second substitution takes place at ortho
and para position. (Study the reactions from Textbook.)
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ˆ Reaction of methyl group in toluene :

CH2C l CHCl2 CCl3
chlorination Cl2/hv Cl2/hv
Cl2 / sunlight –HCl –HCl
384 K
Benzyl chloride Benzal dichloride Benzo trichloride
–HC l

aq. aq. +H2O aq. +2H2O
NaOH –NaC l Ca(OH)2 – 2HC l Ca(OH)2 – 3HC l

CH2OH CHO COOH

CH3
Benzyl alcohol Benzaldehyde Benzoic acid

CHO COOH
Toluene
oxidation KMnO4/ KOH
CrO2Cl2, [O]
Benzaldehyde Benzoic acid

COCH
oxidation
KMnO4 / KOH
Benzoic acid

Conversion : Process to convert one organic compound into another is called organic conversion.
eg, Benzene to benzoic acid.

CH3 COOH
CH3Cl KMnO4/ KOH
[Anhy.AlCl3] [O]
353 K – HCl Toluene Benzoic acid
Benzen

111. Product obtained by complete nitration of toluene is ...... .

(A) o–nitro toluene (B) p–nitro toluene

(C) 2, 4–dinitro toluene (D) 2, 4, 6–trinitro toluene

112. ...... is obtained by reaction of toluene with Cl2 in presence of FeCl3.

(A) m–chloro benzene (B) benzyl chloride

(C) o and p chloro toluene (D) chloro benzene

509

113. ...... is obtained by chlorination of toluene in presence of sunlight .

CH3 CH2Cl CH3 CH3
Cl Cl
(A) (B) (C) (D)
Cl
Cl

114. In Friedel Craft reaction ...... catalyst is used.

(A) anhy.ZnCl2 (B) anhy.AlCl3 (C) FeCl3 (D) CH3Cl

115. What is the function of anhy AlCl3 in Friedel Craft reaction ?
(A) To absorb water. (B) To produce free radical.
(C) To produce electrophilic ion. (D) To produce nucleophilic ion.

116. Methylation of toluene in presence of HF/BF3 gives ...... .
(A) o–xylene (B) p–xylene (C) o and p xylene (D) m–xylene

CH3
KMnO4 / KOH sodalime
117. X Y, X and Y are ...... .
[O]

CHO COOH COOH SO3H

(A) X = Y = (B) X = Y =

COOH CHO

(C) X = Y= (D) X = Y =

Zn CH3COCl
118. X Benzene Y identify X and Y.
anhy AlCl3

(A) X–benzoic acid, Y–toluene (B) X–phenol, Y–toluene
(C) X–phenol, Y–aceto phenone (D) X–toluene, Y–aceto phenone

C2H5Cl ZnO
119. In the reaction P Q final product Q is ...... .
[anhy AlCl3] 903 K
353 K

(A) Benzene (B) m–Xylene (C) ethyl benzene (D) styrene
120. Identify A and B in the following reaction :

H2SO4
CaC2(s) + H2O(1) 
→ A B
HgSO4

(A) A–ethylene B–acetaldehyde (B) A–acetylene B–propanol
(C) A–ethane B–ethanol (D) A–acetylene B–acetaldehyde
510

Instruction : For question no. 121 to 125 for correct sentence T and for incorrect sence F then
select correct option :
121. (i) Each ‘carbon in benzene is sp2 hybridized.
(ii) In benzene C–C bondlength is 154 and 134 para alternatively.
(iii) In benzene 6p electrons are loalized.
(iv) In benzene 6 carbon and 6 hydrogen are identical.
(A) TFFT (B) FTFT (C) TTFF (D) TTTF
122. (i) At normal temperature benzene gives addition reaction with H2, Cl2 and O3 .
(ii) Benzene gives nucleophilic substitution reaction easily.
(iii) Reactivity of benzene is more than alkene.
(A) TFT (B) TTT (C) TTF (D) FFF
123. (i) Benzene is plannar.
(ii) In benzene cyclic shaped molecular orbital of 6p electron.
(iii) Due to resonance reactivity of benzene increases.
(iv) Benzene is insoluble in water.
(A) TTFT (B) TTFF (C) FTTF (D) TTFF
124. (i) –NHCH3 is meta directing group.
(ii) Chlorination of benzoic acid gives O–chloro benzoic acid.
(iii) TNT is used as explosive.
(iv) Ozonolysis of benzene gives addition reaction.
(A) TFFT (B) TTFT (C) FFTT (D) FFTF
125. (i) Chlorobenzene gives Friedel Craft reaction.
(ii) –OH group is electron donor group.
(iii) Nitration of benzene done by nucleophile +NO2.
(iv) Benzene burns with sooty flame.
(A) TTFT (B) TFFF (C) FTTF (D) TFFT
Instruction : Read the paragraph carefully and answer the questions below it.
Paragraph : The compound or ions which follows Huckel’s rule are called aromatic
compounds. Main important point of this law are as follows :
(i) Compound or ion must be plannar.
(ii) It has delocalized p electron coloured.
(iii) p electron cloud should cover all the carbon atom of cyclic system.
(iv) Total number of p e– should be 4n + 2 where n = 0, 1, 2, .....
126. Which of the following compound is not aromatic ?

(A) (B) (C) (D)

127. Which of the following system is aromatic ?

+ + H
(A) (B) (C) (D)

511

128. Which of the following compound is aromatic ?

(A) (B) (C) (D) all

N
S
H
Pyrol Furan Thiofene

ˆ In question 129 to 131 column-I and column-II aer given match them and select correct option :
129. Column-I Column-II

(1) alkane (p) CnH2n–2 (A) (1)−(r), (2)−(q), (3)−(p), (4)−(s)

(2) alkene (q) CnH2n (B) (1)−(p), (2)−(q), (3)−(r), (4)−(s)

(3) alkyne (r) CnH2n+2 (C) (1)−(s), (2)−(r), (3)−(q), (4)−(r)

(4) arene (s) CnH2n–6m (D) (1)−(r), (2)−(s), (3)−(p), (4)−(q)

130. Column-I (Reaction) Column-II (Hydro carbon product)
(a) decarboxylation of sodium acetate (p) ethyne
(b) Wurtz reaction (q) 2–methyl propane
(c) Correy-House reaction (r) n–butane
(d) dehydro halogenation (s) methane

(A) (a)−(r), (b)−(p), (c)−(q), (d)−(s) (B) (a)−(s), (b)−(r), (c)−(q), (d)−(p)
(C) (a)−(q), (b)−(s), (c)−(r), (d)−(p) (D) (a)−(p), (b)−(q), (c)−(s), (d)−(r)
131. Column-I (Reaction) Column-II (Reagent)
(a) CH3COCH3 → CH3CH2CH3 (p) Sodalime

(b) CH3CH2Br → CH2 = CH2 (q) Zn powder

(c) C6H5COOH → C6H6 (r) alcoholic KOH

(d) C6H5OH → C6H6 (s) HI / Red P

(A) (a)−(p), (b)−(s), (c)−(q), (d)−(r) (B) (a)−(q), (b)−(p), (c)−(s), (d)−(r)
(C) (a)−(s), (b)−(r), (c)−(p), (d)−(q) (D) (a)−(s), (b)−(q), (c)−(r), (d)−(p)
ˆ In the following questions two sentences are given out of which one is assertion (A) and
other is reason (R). Study the sentences given below properly and select the open given
below :
(A) Assertion (A) and reason (R) both are correct and reason (R) is correct explanation of
assertion (A).
(B) Assertion (A) and reason (R) both are correct but reason (R) is not correct explanation
of assertion (A).
(C) Assertion (A) is correct while reason (R) is incorrect.
(D) Assertion (A) is incorrect while reason (R) is correct.
512

132. Assertion (A) : Stability of benzene is less than alkene
Reason (R) : Resonance energy of benzene indicates it’s greater stability and less chemical
reactivity.
133. Assertion (A) : cis but–2–ene is polar while trans but-2-ene is non polar.
Reason (R) : In trans isomer both methyl groups are on opposite sides hence net dipole
moment is zero.
134. Assertion (A) : Though benzene has double bond it does not undergo polymerization.
Reason (R) : In normal condition benzene does not behave as alkane.
135. Assertion (A) : Compared to n-pentane boiling point of neo pentane is more.
Reason (R) : neo-pentane has quaternary carbon.
136. Assertion (A) : Dehydration of butan-2-ol mainly gives but-2-ene.
Reason (R) : Dehydration takes place mainly through carbocation intermediate.
137. Assertion (A) : Benzene easily gives electrophilic substitution reaction.
Reason (R) : Benzene is unsaturated hydro carbon.
138. Assertion (A) : By addition reaction of propene with HCl in presence of peroxide mainly gives
2-chloro propane.
Reason (R) : This reaction takes place by free radical intermediate.
139. Assertion (A) : Cyclopenta dienyl anion is more stable than allyl anion.
Reason (R) : Cyclopenta dienyl anion is aromatic.
140. Assertion (A) : Reaction of acetylene with sodamide gives sodium acetylide and ammonia.
Reason (R) : sp hybridized carbon of atoms acetylene are highly electro negative.

Answers : 111. (D), 112. (C), 113. (B), 114. (B), 115. (C), 116. (D), 117. (C), 118. (C),
119. (D), 120. (D), 121. (A), 122. (D), 123. (A), 124. (C), 125. (A), 126. (B),
127. (B), 128. (D), 129. (A), 130. (B), 131. (C), 132. (D), 133. (D), 134. (C),
135. (B), 136. (D), 137. (B), 138. (D), 139. (A), 140. (A).

ˆ

513