Nucleophilic aromatic substitution () via the addition-elimination mechanism requires specific struc — Aromatic Hydrocarbons Chemistry Question
Question
Nucleophilic aromatic substitution ($S_NAr$) via the addition-elimination mechanism requires specific structural features to proceed readily. Which of the following are necessary or highly accelerating factors for this reaction?
💡 Solution & Explanation
$S_NAr$ proceeds via a carbanion intermediate (Meisenheimer complex), not a positively charged arenium ion (which is for electrophilic substitution). It requires a leaving group and is vastly accelerated by strong EWGs (like $-NO_2$) at the ortho and para positions because these groups can accept and delocalize the developing negative charge via extended resonance.