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Enolates & Alpha-Carbon Chemistry
The carbon next to a carbonyl can act as a nucleophile once it loses a proton. You will learn why alpha hydrogens are acidic, how to steer enolate formation, and how aldol, Claisen, and Michael reactions build carbon-carbon bonds.
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What this chapter covers
- Keto-Enol Tautomerism & Alpha Acidity. Alpha hydrogens are unusually acidic, and every aldol, Claisen, and alkylation question starts from that fact.
- Enolate Formation & Alkylation. Choosing the base, temperature, and solvent lets you decide which alpha carbon becomes the nucleophile.
- Aldol Addition & Condensation. The aldol reaction joins two carbonyl compounds through an enolate. Recognizing its product is a classic MCAT skill.
- Claisen, Decarboxylation & Michael Addition. Ester enolates, beta-keto acids, and conjugate additions complete the alpha-carbon toolkit and appear often in synthesis questions.
Key points to know
- Keto and enol forms are tautomers (isomers), not resonance forms
- Alpha-H acidity: β-dicarbonyl ≫ aldehyde > ketone > ester > amide
- LDA at −78 °C makes the kinetic (less substituted) enolate irreversibly
- Weaker base at room temperature gives the thermodynamic (more substituted) enolate
- Aldol addition gives a β-hydroxy carbonyl; condensation gives an α,β-unsaturated carbonyl
- Enolate carbon = nucleophile, carbonyl carbon = electrophile
- Claisen: ester + ester with alkoxide, gives β-keto ester; needs a full equivalent of base
- Dieckmann is an intramolecular Claisen giving 5- or 6-membered rings
Try a practice question
How are a ketone and its enol related?
- They are resonance structures
- They are tautomers, a type of constitutional isomer
- They are enantiomers
- They are conformers
Show the answer
B. Interconversion requires moving a proton, so the two forms are distinct constitutional isomers. Resonance forms differ only in electron placement, never in atom positions.
Common questions
What does this chapter cover?
Enolates & Alpha-Carbon Chemistry covers Keto-Enol Tautomerism & Alpha Acidity, Enolate Formation & Alkylation, Aldol Addition & Condensation, Claisen, Decarboxylation & Michael Addition.
What should I know first?
Keto and enol forms are tautomers (isomers), not resonance forms Alpha-H acidity: β-dicarbonyl ≫ aldehyde > ketone > ester > amide LDA at −78 °C makes the kinetic (less substituted) enolate irreversibly
22 original practice questions accompany this chapter in the app. Spaced review brings missed ideas back at the right time; it helps memory but cannot promise you will not miss an idea again.