Nucleophiles, such as ammonia and its derivatives H2N-Z add to the carbonyl group of aldehydes and ketones. The reaction is reversible and catalyzed by acid. The equilibrium favours the product formation due to rapid dehydration of the intermediate to form -C=N-Z, where ,

Z = Alkyl, aryl, OH, NH₂, C₆H₅NH, NHCONH₂, etc.

What happens when Acetaldehyde reacts with methyl amine? 

Acetaldimine