Haloalkanes and Haloarenes

AIPMT 2005MCQMedium📈 Topic in 50% papers+4−1

Ques. 1AIPMT 2005

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

Ethyl chloride
Isopropyl chloride
Chlorobenzene
Benzyl chloride

Answer

(4) Benzyl chloride

Solution

As per NCERT, SN1 reactions proceed through a carbocation, so halides giving a very stable carbocation react by this path; allylic and benzylic halides show high reactivity towards SN1 because the carbocation is stabilised by resonance.

C6H5CH2Cl C6H5 CH2 + Cl (benzyl carbocation, resonance stabilised)

Ethyl chloride (1°) reacts by SN2; isopropyl chloride (2°) reacts by both SN1 and SN2; chlorobenzene does not undergo nucleophilic substitution under ordinary conditions (partial double bond character of C–Cl).

∴ Benzyl chloride undergoes substitution by SN1 mechanism.

Answer: (4)

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Ques. 2AIPMT 2004

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

(CH3)3C-Cl
CH2=CHCl
CH3CH2Cl
CH2=CHCH2Cl

Ques. 3AIPMT 2004

Chloropicrin is obtained by the reaction of

steam on carbon tetrachloride
nitric acid on chlorobenzene
chlorine on picric acid
nitric acid on chloroform

Out of syllabus

Ques. 4AIPMT 2002

Reactivity order of halides for dehydrohalogenation is

R-F > R-Cl > R-Br > R-I
R-I > R-Br > R-Cl > R-F
R-I > R-Cl > R-Br > R-F
R-F > R-I > R-Br > R-Cl

Ques. 5AIPMT 2001

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

t-butyl chloride
s-butyl chloride
iso-butyl chloride
n-butyl chloride

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