AbstractComparison of the electron impact and chemical ionization mass spectra of N‐substituted‐1H‐azepines and isomeric aromatic substrates reveals significant differences. The data indicate that the substituted azepincs examined are stable to electron impact at low temperatures and retain their antiaromatic 8π electron seven‐membered cyclic system prior to their fragmentation. The electron impact data are supported by low electron‐volt and metastable scan techniques. Electron impact or chemical ionization induced transformation of azepines to aromatic substrates similar to the thermal transformation of neutral analogues is not observed at low temperatures. Chemical ionization mass spectra ofN‐ethoxycarbonyl‐1H‐azepines andN‐phenylcarbamates were complicated owing to thermal decomposition reactions at