Proximity effects in the mass spectra of crowded bis(dimethylamino)arenes: Part II—Rearrangements of the molecular radical cations of ‘proton sponges’ by reciprocal methyl/hydrogen transfer

The EI induced fragmentation pathways of 4,5-bis(dimethylamino)fluorene, 4-(d6-dimethylamino)-5-(dimethylamino)fluorene, 4,5-bis(d6-dimethylamino)fluorene, 4-(dimethylamino)-5-methylaminofluorene, 4,5-bis-(methylamino)fluorene, 4-amino-5-methylaminofluorene, 1,8-bis(dimethylamino)naphthalene, 1,8-bis(d6-dimethyl-amino)-naphthalene and 1,8-bis(dimethylamino)-2,7-dimethoxynaphthalene were investigated. A mechanism is pro-posed for the surprising elimination of CH3NH2 from the molecular ion, followed by loss of C2H5·, C2H4 and CH3CN and for the accompanying cyclizations to stable heterocyclic ions: prior to fragmentation the molecular radical ion rearranges to new, distonic radical ions by reciprocal H and CH3 transfers between the adjacent dimethylamino groups. Each of these new, isomeric molecular ions decomposes subsequently in a characteristic way.