1
MCQ (Single Correct Answer)

AIPMT 2010 Prelims

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.
2
MCQ (Single Correct Answer)

AIPMT 2010 Mains

In the following reaction

the product 'X' is
A
C6H5CH2OCH2C6H5
B
C6H5CH2OH
C
C6H5CH3
D
C6H5CH2CH2C6H5

Explanation

3
MCQ (Single Correct Answer)

AIPMT 2010 Prelims

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.
4
MCQ (Single Correct Answer)

AIPMT 2009

Which of the following reactions is an example of nucleophilic substitution reaction?
A
2RX + 2Na $$ \to $$ R $$-$$ R + 2NaX
B
RX + H2 $$ \to $$ RH + HX
C
RX + Mg $$ \to $$ RMgX
D
RX + KOH $$ \to $$ ROH + KX

Explanation

In nucleophilic substitution, a nucleophile provides an electron pair to the substrate and the leaving group departs with an electron pair.

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