12.19 : 醛和酮与胺：亚胺和烯胺的形成概述

Nitrogen nucleophiles like amines undergo addition reactions with carbonyl compounds.

The addition of a primary amine to an aldehyde or a ketone forms a carbinolamine, which loses water to give an imine, also called a Schiff base.

If, instead, a secondary amine is used, the resulting product will be an enamine.

Imines have a C=N double bond, while enamines possess a C–N single bond and an amino group attached to a C=C double bond.

There are two parts common to the formation of imines and enamines: Generation of carbinolamine and elimination of water. Both reactions form a new C=Nu bond.

The two reactions occur under mild acidic conditions. However, unlike imine formation, enamine formation requires a carbonyl substrate with at least one α hydrogen that can be abstracted in the final elimination step.

Imines are biologically important functional groups. Rhodopsin, a visual pigment in the rods of the retina, is an example of a highly conjugated imine.