Give reasons for the following observations:
i) It is difficult to prepare pure amines by ammonolysis of alkyl halides.
ii) Electrophilic substitution in aromatic amines takes place more readily than in benzene.
i) It is difficult to prepare pure amines by ammonolysis of alkyl halides.
ii) Electrophilic substitution in aromatic amines takes place more readily than in benzene.
Answer: (i) Successive alkylation gives a 1°/2°/3°/quaternary mixture. (ii) The +M –NH₂ group enriches the ring at o/p.
Solution
(i) Each amine formed is itself nucleophilic and attacks more RX — the product is always a mixture of 1°, 2°, 3° amines and the quaternary salt.
(ii) The –NH lone pair delocalises into the ring, raising electron density (most at o/p) — electrophiles attack aniline far faster than benzene (bromine water suffices).
(ii) The –NH lone pair delocalises into the ring, raising electron density (most at o/p) — electrophiles attack aniline far faster than benzene (bromine water suffices).
CBSE Class 12 Board · 2004 · All India Compartment · Subjective