The effect of para-substitution on the mass spectra of arylsulphonate esters of neopentanol

The mass spectra of several para-substituted benzenesulfonic and benzoic esters of unlabelled and 1,1-d₂-neopentyl alcohol are examined and compared. Evidence is presented of migration of the aryl group from the sulfur to an oxygen atom in the molecular ions of the sulfonic esters. The nature of the fragmentation processes and the occurrence of metastable ions for these processes are both much more dependent upon the polarity of the para substituent in the case of the sulfonates than for the benzoates. Elimination of C₅H₁₀ occurs from the molecular ion of the p-methoxysulfonate with transfer to the residual ion of a hydrogen atom selected randomly from the alkyl fragment, while in the case of the p-aminosulfonate, incomplete randomization is demonstrated.