1
MCQ (Single Correct Answer)

AIPMT 2015

In an SN1 reaction on chiral centers, there is
A
inversion more than retention leading to partial racemisation
B
100% retention
C
100% inversion
D
100% racemisation

Explanation

In case of optically active alkyl halides, SN1 reaction is accompanied by racemisation. The carbocation formed in the slow step being sp2 hybridised is planar and attack of nucleophile may take place from either side resulting in a mixture of products, one having the same configuration and other having inverted configuration.

The isomer corresponding to inversion is present in slight excess because SN1 also depends upon the degree of shielding of the front side of the reacting carbon.
2
MCQ (Single Correct Answer)

AIPMT 2015

The possible stereo-structures of CH3CHOHCOOH, which are optically active, are called
A
atropisomers
B
enantiomers
C
mesomers
D
diastereomers

Explanation

They are enantiomers (non-superimposable mirror images)
3
MCQ (Single Correct Answer)

AIPMT 2014

Which of the following compounds will undergo racemisation when solution of KOH hydrolyses?
A
(i) and (ii)
B
(ii) and (iv)
C
(iv)
D
(i) and (iv)

Explanation

Out of the given four compounds only (iv) compound is chiral and hence only this compound will undergo racemisation.
4
MCQ (Single Correct Answer)

NEET 2013 (Karnataka)

Given :

I and II are
A
identical
B
a pair of conformers
C
a pair of geometrical isomers
D
a pair of optical isomers

Explanation

Conformers are form of stereoisomers in which isomers can be interconverted by rotation about single bonds. I and II are staggered and eclipsed conformers respectively.

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