On treatment with strong acid, pyrrole is protonated mainly at C-2 rather than at nitrogen because

Aprotonation at N would remove the nitrogen lone pair from the aromatic sextet, whereas C-2 protonation gives a resonance-stabilised cation
Bthe nitrogen has no lone pair
CC-2 is more electronegative than N
Dprotonation at N is sterically impossible

Answer: A

The lone pair on pyrrole nitrogen is part of the aromatic sextet. Protonation at C-2 gives a cation in which the N lone pair stabilises the charge through an iminium-type resonance form (

C = N X^{+}

); N-protonation would give a non-aromatic ammonium-like species. This is why pyrrole is a very weak base (pKaH about

- 3.8

) and is sensitive to acid.

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On treatment with strong acid, pyrrole is protonated mainly at C-2 rather than at nitrogen because

Answer: A

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