Aldol addition
Connecting the α-carbon of one with the carbonyl carbon of the other.
- The carbonyl carbon of an aldehyde or ketone is an electrophile, and when the proton is removed from the α-carbon, the α-carbon can be an nucleophile.
- An aldol addition is a reaction in which both of these reactivities are observed.
When the reactant is an aldehyde,
the product is a β-hydroxyaldehyde.
When the reactant is a ketone,
the product is a β-hydroxyketone.
Aldol condensation
When the product of an aldol addition is dehydrated, the overall reaction is called an aldol condensation.
- Unlike alcohols that can be dehydrated only under acidic conditions, β-hydroxyaldehydes and β-hydroxyketones can also be dehydrated under basic conditions.
- Reaction proceeds via E1cB ,a two-step elimination reaction that forms a carbanion intermediate.
An aldol condensation forms
an α,β-unsaturated aldehyde or
an α,β-unsaturated ketone, called enones.
