Enols: Alpha Substitution and Halogenation
Start with the big picture
The lesson connects α-hydrogen acidity with formation of the enol and enolate intermediates used in carbonyl α-substitution. In acid-catalyzed reactions, the enol acts as the nucleophile; under basic conditions, the enolate is formed and reacts with an electrophile. The mechanisms differ in their sequence and commonly rate-determining step. Halogenation illustrates how conditions affect product formation: acidic conditions usually favor monohalogenation, whereas basic conditions can allow repeated substitution. The topic also introduces the haloform reaction of methyl ketones and considers enolate regioselectivity, including the contrast between thermodynamic and kinetic enolates. Together, these ideas provide a framework for understanding how reaction conditions influence α-substitution outcomes.
What you'll learn
- Explain how α-hydrogen acidity enables enol and enolate formation.
- Distinguish acid-catalyzed and base-catalyzed α-substitution mechanisms.
- Compare α-halogenation outcomes under acidic and basic conditions.
- Describe the haloform reaction of methyl ketones.
- Relate base choice to kinetic or thermodynamic enolate formation.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
