Specific and random fragmentations in the mass spectra of some neopentyl compounds

The mass spectra of neopentyl alcohol, bromide and chloride and some ¹³C and ²H labelled analogues have been studied. Most fragmentations of the molecular ions of these compounds occur by simple bond cleavages and do not involve rearrangement before fragmentation. We propose that in the M ? CH₃]⁺ fragment ions, seven of the eight hydrogen atoms and all four carbon atoms are involved in randomisation when an ethylene molecule is ejected. The eighth hydrogen atom (which comes from a methyl group) is probably associated with the heteroatom. The neopentylcation, observed only in the mass spectrum of the bromide, fragments mainly by loss of an ethylene molecule, also containing randomly selected hydrogen and carbon atoms. The C₄H₇]⁺ ion also was observed to undergo complete atom scrambling.