1

### 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.
2

### AIPMT 2003

Which of the following pairs of compounds are enantiomers?
A
B
C
D

## Explanation

These two are non-superimposable mirror images of each other, so they are enantiomers.
3

### AIPMT 2002

Z in the above reaction sequence is
A
CH3CH2CH2NHCOCH3
B
CH3CH2CH2NH2
C
CH3CH2CH2CONHCH3
D
CH3CH2CH2CONHCOCH3

## Explanation

4

### AIPMT 2002

Reactivity order of halides for dehydrologenation is
A
$R - F > R - Cl > R - Br > R - {\rm I}$
B
$R - {\rm I} > R - Br > R - Cl > R - F$
C
$R - {\rm I} > R - Cl > R - Br > R - F$
D
$R - F > R - {\rm I} > R - Br > R - Cl$

## Explanation

I > Br > Cl > F

F, Cl, Br, I belongs to the same group orderly. Atomic radii go on increasing as the nuclear charge increases from top to bottom in a group. The decreasing order of bond length C – I > C – Br > C – Cl > C – F. The order of bond dissociation energy
R – F > R – Cl > R – Br > R – I. During dehydrohalogenation C – I bond breaks more easily than C – F bond.So reactivity order of halides

$R - {\rm I} > R - Br > R - Cl > R - F$