Consider the reactions.
The mechanisms of reactions (i) and (ii) are respectively
A
SN1 and SN2
B
SN1 and SN1
C
SN2 and SN2
D
SN2 and SN1
Explanation
These reactions are purely SN2
reactions as in
reaction (i) and (ii) there is no rearrangement takes
place (rearrangement occurs in SN1
mechanism).
Simple substitution of nucleophile takes place.
2
AIPMT 2010 Prelims
MCQ (Single Correct Answer)
The correct order of increasing reactivity of
C$$-$$X bond towards nucleophile in the following compounds is
A
I < II < IV < III
B
II < III < I < IV
C
IV < III < I < II
D
III < II < I < IV
Explanation
The order of reactivity is dependent on the
stability of the intermediate carbocation formed by
cleavage of C—X bond. The 3° carbocation formed
in III will be more stable than its 2° homologue (IV)
which in turn will be more stable than arenium
ion (I). Moreover, the aryl halide has a double
bond character in the C—X bond which makes
the cleavage more difficult. On other hand II will
be more reactive than I due to presence of electron
withdrawing —NO2 group. C—X bond becomes
weak and undergoes nucleophilic substitution
reaction
So Correct order is I < II < IV < III.
3
AIPMT 2010 Mains
MCQ (Single Correct Answer)
In the following reaction
the product 'X' is
A
C6H5CH2OCH2C6H5
B
C6H5CH2OH
C
C6H5CH3
D
C6H5CH2CH2C6H5
Explanation
4
AIPMT 2010 Prelims
MCQ (Single Correct Answer)
Which one is most reactive towards SN1 reaction?
A
C6H5CH(C6H5)Br
B
C6H5CH(CH3)Br
C
C6H5C(CH3)(C6H5)Br
D
C6H5CH2Br
Explanation
SN1 reactions involve the formation of
carbocations, hence higher the stability of
intermediate carbocation, more will be reactivity
of the parent alkyl halide. The tertiary carbocation
formed from (c) is stabilized by two phenyl groups
and one methyl group, hence most stable.
Questions Asked from Haloalkanes and Haloarenes
On those following papers in MCQ (Single Correct Answer)
Number in Brackets after Paper Indicates No. of Questions
