An N-nitrosamine is a compound that has the following general structural formula.
R1 and R2 could be hydrogen atoms, alkyl groups, aryl groups, or any combination thereof.
An N-nitrosamine is stable only if neither R1 nor R2 is a hydrogen atom. Thus, 1 is unstable, and 2 and 3 are stable. 1 exists mostly as the tautomer (4), which is called a diazotic acid.
see also nitroso group