Pyridine is highly deactivated towards electrophilic aromatic substitution compared to benzene. When forced under drastic conditions, at which position does the electrophile predominantly attack, and

Question

Pyridine is highly deactivated towards electrophilic aromatic substitution compared to benzene. When forced under drastic conditions, at which position does the electrophile predominantly attack, and why?

Prashant Kotian · Accepted Answer

Correct answer: B. In pyridine, the highly electronegative nitrogen atom severely deactivates the ring. If an electrophile attacks at C-2 or C-4, one of the resulting resonance structures places a formal positive charge on the highly electronegative nitrogen atom with only a sextet of electrons (a highly unstable divalent positive nitrogen). Attack at C-3 entirely avoids this unfavorable resonance structure, making the C-3 intermediate relatively more stable, though still highly deactivated compared to benzene.

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