Question

How will you detect you the presence of -NO2 group in benzene ring.

Answer 1

Presence of a nitro group in a benzene ring

(a) deactivates the ring towards electrophilic substitution

(b) activates the ring towards electrophilic substitution

(c) renders the ring basic

(d) deactivates the ring towards nucleophilic substitution

Answer 2

Explanation:

1. To the alcoholic solution of nitro benzene add ammonium chloride with sum pinch of zinc dust and heat for 5 minutes.

Nitro group get reduced to hydroxylamine in presence of mild reducing agent.

$Ph-NO_2+4H\overset{ZN-dust+NH_4Cl}\rightarrow Ph-NH-OH+H_2O$

2.After heating the solution filter it out and to the filtrate add Tollen's reagent.

Tollen's reagent = Silver ammonical nitrate

The hydroxylamine formed reduces Tollen's reagent and get oxidized to nitroso compound.

$Ph-NH-OH+2[Ag(NH_3)_2]OH\rightarrow PhNO+4NH_3+2H_2O+Ag(ppt)$

Formation of grey precipitate turning black indicates that nitro group was present.