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Haloalkanes and Haloarenes · Question 31

AIPMT 2008MCQEasy📈 Topic in 50% papers+4−1
1

In an SN2 substitution reaction of the type R-Br + Cl- DMF R-Cl + Br- which one of the following has the highest relative rate?

  1. CH3- CH3 | CH3 |C-CH2Br
  2. CH3CH2Br
  3. CH3CH2CH2Br
  4. CH3- CH3 |CH-CH2Br

Answer

(2) CH3CH2Br

Solution

As per NCERT, in an SN2 reaction the nucleophile attacks the carbon from the side opposite to the leaving group; bulky groups on or near this carbon hinder the attack and slow the reaction.

All four are primary bromides, so the rate depends on the crowding near the -CH2Br carbon.

CH3CH2Br has the smallest alkyl group; CH3CH2CH2Br is slightly more hindered; branching at the β-carbon in (CH3)2CHCH2Br and especially in (CH3)3CCH2Br blocks the back-side attack.

Relative rate: CH3CH2Br > CH3CH2CH2Br > (CH3)2CHCH2Br > (CH3)3CCH2Br

Answer: (2)

AIPMT 2008

Keep practising — Haloalkanes and Haloarenes

2

Which of the following undergoes nucleophilic substitution exclusively by SN1 mechanism?

  1. Ethyl chloride
  2. Isopropyl chloride
  3. Chlorobenzene
  4. Benzyl chloride
AIPMT 2005
3

Which of the following is least reactive in a nucleophilic substitution reaction?

  1. (CH3)3C-Cl
  2. CH2=CHCl
  3. CH3CH2Cl
  4. CH2=CHCH2Cl
AIPMT 2004
4

Chloropicrin is obtained by the reaction of

  1. steam on carbon tetrachloride
  2. nitric acid on chlorobenzene
  3. chlorine on picric acid
  4. nitric acid on chloroform
Out of syllabusAIPMT 2004
5

Reactivity order of halides for dehydrohalogenation is

  1. R-F > R-Cl > R-Br > R-I
  2. R-I > R-Br > R-Cl > R-F
  3. R-I > R-Cl > R-Br > R-F
  4. R-F > R-I > R-Br > R-Cl
AIPMT 2002
6

An organic compound A (C4H9Cl) on reaction with Na/diethyl ether gives a hydrocarbon which on monochlorination gives only one chloro derivative, then A is

  1. t-butyl chloride
  2. s-butyl chloride
  3. iso-butyl chloride
  4. n-butyl chloride
AIPMT 2001

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