1

### AIPMT 2007

If there is no rotation of plane polarised light by a compound in a specific solvent, through to be chiral, it may mean than
A
the compound is certainly meso
B
there is no compound in the solvent
C
the compound may be a racemic mixture
D
the compound is certainly a chiral.

## Explanation

Compounds which do not show optical activity inspite of the presence of chiral carbon atoms are called meso-compounds. The absence of optical activity in these compound is due to the presence of a plane of symmetry in their molecules. e.g. meso-tartaric acid is optically inactive.
2

### AIPMT 2007

CH3 $-$ CHCl $-$ CH2 $-$ CH3 has a chiral centre. Which one of the following represents its R-configuration?
A
B
C
D

## Explanation

3

### AIPMT 2006

Which of the following is not chiral?
A
2-Hydroxypropanoic acid
B
2-Butanol
C
2,3-Dibromopentane
D
3-Bromopentane

## Explanation

Due to absence of asymmetric carbon atom.
4

### AIPMT 2004

Which of the following is least reactive in a nucleophilic sibstitution reaction?
A
(CH3)3C $-$ Cl
B
CH2$=$CHCl
C
CH3CH2Cl
D
CH2$=$CHCH2Cl

## Explanation

Chlorine of vinyl chloride (CH2==CHCl) is non-reactive substitution reaction because it shows the following resonating structure due to +M effect of –Cl atom.

In second Cl–atom has positive charge and partial double bond character with C of vinyl group, so it is more tightly attracted towards the nucleus and it does not get replaced by nucleophile in nucleophilic substitution reaction.