a-Substitution and Carbonyl Condensation Reactions Alpha-substitution reactions occur at the carbon next to the carbonyl carbon-the a position Involve substitution of a-hydrogen :9: An enolate ion by electrophile Proceed through enol or enolate ion intermediate A carbonyl An alpha-substituted compound carbonyl compound Carbonyl condensation reactions occur between two carbonyl An enol partners Combination of a-substitution and nucleophilic addition steps i- New C-C bond Gives B-hydroxy carbonyl compound A carbonyl An enolate A B-hydroxy compound ion carbonyl compoundAlpha-substitution reactions occur at the carbon next to the carbonyl carbon – the a position ▪ Involve substitution of a-hydrogen by electrophile ▪ Proceed through enol or enolate ion intermediate Carbonyl condensation reactions occur between two carbonyl partners ▪ Combination of a-substitution and nucleophilic addition steps ▪ Gives b-hydroxy carbonyl compound α-Substitution and Carbonyl Condensation Reactions