1
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.
2
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.
3
MCQ (Single Correct Answer)

AIPMT 2008

In a SN2 substitution reaction of the type
R $$-$$ Br + Cl$$-$$ $$\buildrel {DMF} \over \longrightarrow $$ R$$-$$Cl + Br$$-$$
which one of the following has the highest relative rate?
A
B
CH3CH2Br
C
CH3CH2CH2Br
D

Explanation

SN2 mechanism is followed in case of primary and secondary halides i.e., SN2 reaction is favoured by small groups on the carbon atom attached to halogens so

CH3 – X > R – CH2 – X > R2CH – X > R3C – X
4
MCQ (Single Correct Answer)

AIPMT 2008

How many stereoisomers does this molecule have?

CH3CH$$=$$CHCH2CHBrCH3
A
8
B
2
C
4
D
6

Explanation



Both geometrical isomerism (cis-trans form) and optical isomerism is possible in the given compound.

No. of optical isomer = 2n = 21 = 2
(where n = no. of asymmetric carbon)

Hence total no. of stereoisomers = 2 + 2 = 4

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