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Hydrocarbons · Question 49

AIPMT 2005MCQMedium📈 Topic in 62% papers+4−1
1

Which one of the following alkenes will react faster with H2 under catalytic hydrogenation conditions ?

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]

Answer

(1) [figure]

Solution

In catalytic hydrogenation, the alkene is adsorbed on the metal surface and both H atoms are added from the same side (syn addition).

∵ Bulky R groups on the double bond hinder its approach to the catalyst surface, the rate decreases as substitution increases; a more substituted alkene is also more stable (lower heat of hydrogenation).

⇒ Rate of hydrogenation: less substituted > more substituted, i.e. disubstituted > trisubstituted > tetrasubstituted

Among the two disubstituted alkenes, in the cis-1,2-disubstituted alkene (option 1) each doubly bonded carbon carries only one R group, so neither carbon is crowded (in option 2 one carbon carries both R groups); it is also the less stable of the two and reacts faster.

∴ The alkene in option (1) reacts fastest.

Answer: (1)

AIPMT 2005

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2

Products of the following reaction : CH3C CCH2CH3 [(ii) hydrolysis](i) O3 are

  1. CH3COOH + CO2
  2. CH3COOH + HOOC.CH2CH3
  3. CH3CHO + CH3CH2CHO
  4. CH3COOH + CH3COCH3
AIPMT 2005
3

Using anhydrous AlCl3 as catalyst, which one of the following reactions produces ethylbenzene (PhEt)?

  1. H3C-CH2OH + C6H6
  2. CH3-CH=CH2 + C6H6
  3. H2C=CH2 + C6H6
  4. H3C-CH3 + C6H6
AIPMT 2004
4

Reaction of HBr with propene in the presence of peroxide gives

  1. isopropyl bromide
  2. 3-bromopropane
  3. allyl bromide
  4. n-propyl bromide
AIPMT 2004
5

The compound CH3- CH3 |C=CH-CH3 on reaction with NaIO4 in the presence of KMnO4 gives

  1. CH3COCH3
  2. CH3COCH3 + CH3COOH
  3. CH3COCH3 + CH3CHO
  4. CH3CHO + CO2
AIPMT 2003
6

The correct order of reactivity towards the electrophilic substitution of the compounds aniline (I), benzene (II) and nitrobenzene (III) is

  1. III > II > I
  2. II > III > I
  3. I < II > III
  4. I > II > III
AIPMT 2003
7

When CH3CH2CHCl2 is treated with NaNH2, the product formed is

  1. CH3-CH=CH2
  2. CH3-C CH
  3. [figure]
  4. [figure]
AIPMT 2002
8

Which alkene on ozonolysis gives CH3CH2CHO and CH3COCH3?

  1. [figure]
  2. CH3CH2CH=CHCH2CH3
  3. CH3CH2CH=CHCH3
  4. [figure]
AIPMT 2001
9

Increasing order of electrophilic substitution for following compounds [figure]

  1. IV < I < II < III
  2. III < II < I < IV
  3. I < IV < III < II
  4. II < III < I < IV
AIPMT 2000
10

In Friedel-Crafts reaction, toluene can be prepared by

  1. C6H6 + CH3Cl
  2. C6H5Cl + CH4
  3. C6H6 + CH2Cl2
  4. C6H6 + CH3COCl
AIPMT 2000

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