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Question
Why does acetylation of –NH2 group of aniline reduce its activating effect?
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Solution
Direct nitration of aniline is not possible on account of oxidation of –NH2 group. However, nitration can be carried after protecting the –NH2 group by acetylation to give acetanilide which is then nitrated and finally hydrolysed to give o- and p-nitroanilines.
The acetyl group being electron-withdrawing attracts the lone pair of electrons of the N-atom towards carbonyl group.
As a result, the activating effect –NH2 group is reduced i.e., the lone pair of electrons on nitrogen is less available for donation to benzene ring by resonance. Therefore, activating effect of –NHCOCH3 group is less than that of –NH2 group.
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