Some aspects of the mass spectra of triptycene and tri‐ and diphenylmethanes

Mass spectra of isotope‐labeled triptycenes, triphenylmethanes and diphenylmethanes rule out the bulk of postulated decomposition mechanisms and fragment‐ion structures. The formation of [M H] + and [M 2H] 2+ from triptycene, of [M H] + , [M CH 3 ] + and [M CH 4 ] + from triphenylmethane, and of [M H] 2+ and [M 2H] 2+ ‐as well as the previously reported [M H] + and [M CH 3 ] + ‐from diphenylmethane all seem to be preceded or accompanied by complete loss of position identity of the α and ring hydrogens in the original molecules. A statistical preference for loss of α hydrogens is found in the process leading to [M 2H] + and [M H] 2+ from triptycene, as in the formation of [M H] 2+ from toluene.