OrgoChem II

Enolates Aldol and Claisen

Alpha chemistry carbon carbon bond building

Summary

Identify alpha position choose base and conditions then build CC bonds. Full reference is on the external link.

What you need to know:

This topic covers enolates aldol and claisen. Focus on mastering the key concepts in the "Must know checklist" below. Follow the study steps systematically, and use practice problems to reinforce your understanding. The external reference provides comprehensive coverage of all concepts.

Video Tutorial

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Aldol Addition Reactions, Intramolecular Aldol Condensation Reactions

Click to watch on YouTube →

Must know checklist

0 / 5 complete

Alpha hydrogen acidityα-H's are acidic (pKa ~20 for ketones, ~25 for esters) due to enolate resonance; stronger base (LDA, NaH) → enolate; weaker base (OH-) → enol equilibrium
Aldol Addition Reactions, Intramolecular Aldol Condensation→
Kinetic vs thermodynamic enolatekinetic (LDA, low temp) attacks less substituted α-C; thermodynamic (strong base, high temp) attacks more substituted α-C (more stable enolate)
Enolate Formation - Alpha Hydrogen Acidity→
Aldol reactionenolate + carbonyl → β-hydroxy carbonyl (aldol addition); with heat/base → α,β-unsaturated carbonyl (aldol condensation); can be intramolecular
Kinetic vs Thermodynamic Enolate Control→
Claisen condensationester enolate + ester → β-ketoester; requires: 2 α-H's, matching alkoxide base (R'O- for R'CO2R'), full equivalent of base (consumed in second deprotonation)
Claisen Condensation Mechanism - Beta-Ketoester Formation→
Michael additionenolate (donor) + α,β-unsaturated carbonyl (acceptor) → 1,4-addition (conjugate addition); forms new C-C bond β to carbonyl; enolate attacks β-carbon
Michael Addition - Conjugate Addition of Enolates→

Common mistakes

Using wrong base alkoxide in Claisen (must match ester R group)

Not checking alpha position before enolate formation

Mixing up kinetic (LDA, less substituted) vs thermodynamic enolate