α‑Halogenation of Carbonyls: Acid vs Base Conditions (Mono vs Poly-halogenation)

Learn α‑halogenation mechanisms via enol/enolate pathways. Predict mono vs poly-halogenation, and connect to the haloform reaction.

• Reaction: Carbonyl → α-halocarbonyl
• What it does: Installs halogen at the alpha position
• Typical reagents: Acid: Br2/H+ (mono). Base: Br2/OH− (often poly, can lead to haloform with methyl ketones)
• Key intermediate: Enol (acid) or enolate (base)
• Driving force: Formation of C–X bond; under base, acidity increases after each halogenation
• Exam type: Mechanism choice (enol vs enolate)
• Exam type: Predict product