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15.28: Aldol Condensation vs Claisen Condensation

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Organic Chemistry

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Aldol Condensation vs Claisen Condensation

15.28: Aldol Condensation vs Claisen Condensation

Aldol condensation is an acid or base-catalyzed condensation between aldehydes or ketones to give an α,ꞵ-unsaturated carbonyl compound. A base-promoted condensation between ester molecules to produce a ꞵ-ketoester is known as the Claisen condensation. In the presence of a base, both reactions involve deprotonation of the acidic α hydrogen to produce the corresponding enolates. The nucleophilic enolates attack their respective nonenolized carbonyl compound forming a tetrahedral intermediate.


The resulting intermediates of aldol and Claisen condensation undergo different pathways. In aldol condensation, the alkoxide intermediate gets protonated to give an addition product, the ꞵ-hydroxy carbonyl compound. In Claisen condensation, the intermediate expels the alkoxide group, thereby restoring C=O and producing a nucleophilic acyl substituted 1,3-dicarbonyl compound.

In the final step, the addition product at an elevated temperature undergoes dehydration to form α,ꞵ-unsaturated carbonyl compound. While in Claisen condensation, the acyl substituted molecule undergoes irreversible deprotonation followed by acidification yielding a ꞵ-ketoester.


Aldol Condensation Claisen Condensation Acid-catalyzed Condensation Base-catalyzed Condensation Aldehydes Ketones α,β-unsaturated Carbonyl Compound Ester Molecules β-ketoester Enolates Nucleophilic Attack Tetrahedral Intermediate Alkoxide Intermediate Addition Product α-hydroxy Carbonyl Compound Nucleophilic Acyl Substituted 1,3-dicarbonyl Compound Dehydration Irreversible Deprotonation Acidification

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