In organic chemistry, aldol reactions are acid- or base-catalyzed reactions of aldehydes or ketones.
Aldol addition or aldolization refers to the addition of an enolate or enolation as a nucleophile to a carbonyl moiety as an electrophile. This produces a β-hydroxyaldehyde or β-hydroxyketone. In an aldol condensation, water is subsequently eliminated and an α,β-unsaturated carbonyl is formed. The aldol cleavage or Retro-aldol reaction is the reverse reaction into the starting compounds.
The name aldehyde -alcohol reaction derives from the reaction product in the case of a reaction among aldehydes, a β-hydroxy aldehyde.
Aldol reactions are important reactions for carbon-carbon bond formation and a fundamental reaction principle in organic chemistry.