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1

### 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.
2

### AIPMT 2012 Mains

In the replacement reaction

The reaction will be most favourable if M happens to be
A
Na
B
K
C
Rb
D
Li

## Explanation

Tertiary alkyl halides shows SN1 mechanism to the greater extent. In the given reaction negative ion will attack on carbocation. Thus, greater the tendency of ionization (greater ionic character in M-F bond) more favourable will be reaction. In the given options Rb-F is most ionic and hence it will be most favourable for SN1 mechanism.
3

### AIPMT 2011 Mains

Consider the reactions.

The mechanisms of reactions (i) and (ii) are respectively
A
SN1   and  SN2
B
SN1   and  SN1
C
SN2   and  SN2
D
SN2   and  SN1

## Explanation

These reactions are purely SN2 reactions as in reaction (i) and (ii) there is no rearrangement takes place (rearrangement occurs in SN1 mechanism). Simple substitution of nucleophile takes place.
4

### 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.

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Class 12