ORIGIN OF [M-IMPACT MASS-SPECTRA OF TERTIARY NITROSONITRILES(H](+) IONS IN ELECTRON)

The presence of [M + H](+) ions was observed in the electron impact ma ss spectra of the series of dimers of aliphatic tertiary beta-, gamma- and delta-nitrosonitriles. Neither M(+.) nor [M + H](+) ions are obse rved in the spectra of alpha-nitrosonitriles or after introduction of voluminous substituents into the molecule, so the geometric factor is very important. It was found that this effect was probably due to the rearrangement of the hydrogen atom in the fragmentation pattern of the dimer molecular ions 2M(+.) of beta- and delta-nitrosonitriles. Aliph atic nitrosocompounds exist even in the gas phase in equilibrium with their dimers. The existence of dimers was confirmed by the presence of the [2M + H](+.) ion in the liquid secondary ion mass spectrum of a g amma-nitrosonitrile. Using deuterium labelling, as distinct to the nit rosoketones and esters, it was unexpectedly found that the origin of h ydrogen in the [M + H](+) ions was the methyl groups in the position v icinal to the tertiary nitroso group (CH3)(2)C(NO)R.