In the electron impact mass spectra of N , N ′‐diaryl‐1,3‐phenylenediamines, recorded under conditions generating the molecular ion as a base peak, the most important step involve a β‐aromatic cleavage with H rearrangement, leading to the expulsion of a neutral arylamine; this fact can be used in meta isomer identification since for the corresponding 1,2‐ and 1,4‐isomers the expulsion of an aryl radical is a competitive process