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.

eg:

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, which is called a diazotic acid.

see also nitroso group