Topic overview

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An enolate, formed by removing an α-hydrogen, acts as the nucleophile that initiates carbonyl condensation reactions. In an aldol reaction, it adds to a carbonyl to form a β-hydroxy carbonyl, which may dehydrate to an α,β-unsaturated carbonyl. Claisen condensation forms β-keto esters, while its intramolecular counterpart, the Dieckmann condensation, forms cyclic β-keto esters. Michael addition creates a C–C bond by conjugate addition at the β-carbon; combined with intramolecular aldol chemistry, it can form the basis of a Robinson annulation. Reactant structure, base choice, product stabilization, and possible reverse reactions all shape these pathways. The deeper lesson compares mechanisms and practical considerations across the reaction types.