Enamine formation: practice and mechanism
A secondary amine (pyrrolidine) adds to the carbonyl group. It cannot form an imine (no second H on N), so an H is lost from the α-carbon instead: an enamine (C=C–N) forms.
Example
A secondary amine adds to the carbonyl group and water is lost. Because the nitrogen has no H left, no imine can form; instead an H is lost from the α carbon, giving an enamine (N–C=C).
Mechanism step by step
- 1
The secondary amine attacks the carbonyl carbon; after proton transfer a hemiaminal forms.
- 2
The acid protonates the OH group and water leaves: an iminium ion (C=N⁺R₂) forms.
- 3
The N has no H to give, so an H is removed from the α-carbon: enamine (C=C–NR₂).
Practice tasks
Which product forms, which reagent is needed? After each answer you see the explanation.
Which main product forms?
Typical mistakes
Often confused with: Imine formation
Frequently asked questions
What are enamines good for?
The α-carbon is nucleophilic (like an enolate but neutral and milder). Stork enamine reaction: alkylation or Michael addition, then hydrolysis back to the ketone.
Imine or enamine?
Primary amine (RNH₂) → imine (C=N–R). Secondary amine (R₂NH) → enamine, because there is no H left on N.