1
MCQ (Single Correct Answer)

AIPMT 2011 Mains

Which of the following compounds undergoes nucleophilic substitution reaction most easily?
A
B
C
D

Explanation

Electron withdrawing group like -NO2 facilitates nucleophilic substitution reaction in chlorobenzene.
2
MCQ (Single Correct Answer)

AIPMT 2011 Prelims

The Lassaigne's extract is boiled with conc. HNO3 while testing for halogens. By doing so it
A
decomposes Na2S and NaCN, formed
B
helps in the precipitation of AgCl
C
increases the solubility product of AgCl
D
increases the concentration of N$$_3^ - $$ ions

Explanation

In case of Lassaigne’s test of halogens, it is necessary to remove NaCN and Na2S from the sodium extract, if nitrogen and sulphur are present. This is done by boiling the sodium extract with conc. HNO3.

NaCN + HNO3 $$ \to $$ NaNO3 + HCN $$ \uparrow $$

Na2S + 2HNO3 $$ \to $$ 2NaNO3 + H2S $$ \uparrow $$
3
MCQ (Single Correct Answer)

AIPMT 2011 Prelims

Which one is a nucleophilic substitution reaction among the following ?
A
B
C
D

Explanation

Because of high electronegativities of the halogen atom, the carbon halogen (C – X) is highly polarised covalent bond. Thus, the carbon atom of the C – X bond becomes a good site for attack by nucleophiles (electron rich species). Nucleophilic substitution reactions are the most common reactions of alkyl halides.
4
MCQ (Single Correct Answer)

AIPMT 2011 Prelims

Which one of the following is most reactive towards electrophilic reagent?
A
B
C
D

Explanation

+R effect of -OH group is greater than of -OCH3 group. That is why it is highly reactive towards electrophilic substitutions.

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