In organic chemistry, an imine is a chemical compound that has a carbon atom with a double bond to a nitrogen atom.^[1] The C=N functional group is called imino.

Imines are divided into primary and secondary imines based on what else is connected to the nitrogen atom. If nitrogen is connected to hydrogen, it is a primary imine. If it is connected to carbon, it is a secondary imine.

Imines are also divided into groups depending on what the carbon is connected to. If it is connected to two other carbons, it is a ketimine (like a ketone).^[2] If it is connected to hydrogen, it is an aldimine (like an aldehyde).^[3]

Imines are made by a condensation reaction between carbonyl compounds and ammonia or primary amines. Different types of ingredient give different types of imine: ketones give ketimines, aldehydes give aldimines, ammonia gives primary imines, and primary amines give secondary imines. This reaction makes water as a byproduct.^[4]

This condensation is reversible: an imine and a water molecule can react, breaking the imine apart into the original ingredients. (Breaking a molecule up with water is called hydrolysis.) Something needs to remove the water in order to keep the reaction going. This can be a process like distillation, or an added desiccant.