Aldol condensation

A carbon–carbon bond-forming reaction in which an enolate adds to a carbonyl compound, often followed by dehydration to form an α,β-unsaturated carbonyl compound.

Enolate: A resonance-stabilized anion formed by removing an α-hydrogen from a carbonyl compound. It acts as the carbon nucleophile that initiates the bond-forming step.
Carbonyl group: A functional group consisting of a carbon atom double-bonded to an oxygen atom. Its polarized bond makes carbonyl carbons electrophilic and α-hydrogens enolizable.
Crossed aldol reaction: An aldol reaction between two different carbonyl compounds. It extends the reaction to construct products from unlike carbonyl partners.
Claisen condensation: A carbon–carbon bond-forming reaction in which an ester enolate acylates another ester, producing a β-keto ester. It resembles aldol chemistry but forms a carbon–carbon bond by acyl substitution.
Aldol addition: The addition of an enolate to a carbonyl compound to form a β-hydroxy carbonyl compound. This is the bond-forming stage before any dehydration occurs.
α-Carbon: The carbon atom directly adjacent to a functional group, especially a carbonyl group. Removing an α-hydrogen enables the nucleophilic enolate to form.
Directed aldol reaction: An aldol reaction in which a preformed enolate is combined with a chosen carbonyl electrophile. Preforming the enolate helps control which partner supplies the nucleophilic carbon.
Michael addition: Conjugate nucleophilic addition to an electron-poor alkene, commonly an α,β-unsaturated carbonyl compound. It forms carbon–carbon bonds by attack at an alkene rather than direct carbonyl addition.
E1cB elimination: An elimination pathway in which deprotonation forms a carbanion before a leaving group departs. It commonly accounts for dehydration of the aldol product under basic conditions.
Keto–enol tautomerism: The interconversion of a carbonyl compound and its enol through proton transfer and bond rearrangement. Enolate formation is related to deprotonation at the same site involved in enolization.

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