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Consider the two resonance structures drawn for pyrrole. Structure II shows the nitrogen lone pair delocalized into the ring, giving nitrogen a positive charge and a ring carbon a negative charge. Which statement about structure II is correct?

1. II is not acceptable because a carbonium ion is less stable than a nitride ion
2. II is not acceptable because it involves charge separation
3. II is not acceptable because nitrogen would have ten valence electrons
4. II is an acceptable resonating structure

Correct answer: II is an acceptable resonating structure

Solution

In pyrrole, nitrogen donates its lone pair into the aromatic ring. The resulting charge-separated structure (N positive, ring C negative) keeps nitrogen with a complete octet (8 electrons, not 10) and is a legitimate contributing resonance structure. Charge separation alone does not make a structure unacceptable.

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