The unimolecular metastable ion dissociations of o-trimethylsilyl toluate, o-CH3C6H4COOSi(CH3)3 (1) and its fluorine analogue, o-trimethylsilyl ~,~,ot-trifluorotoluate, o-CF3C6H4COOSi(CH3)3 (2), upon electron impact, have been investigated by means of B/E linked scan and high resolution data. The fragmentation processes of these compounds were elucidated with the aid of those of the corresponding acids, o-toluic acid, o-CH3C6H4COOH (3) and o-s, ~, c~-trifluorotoluic acid, o-CF3C6H4COOH (4), respectively.
No molecular ion is observed for 2, but a fairly abundant molecular ion is observed for 1. The fragmentation of 1 Γ·. is different from that of 2", except for the loss of "CH3 from the respective molecular ions. In the case of 1, (CH3)3SiOH is eliminated from 1 + with the migration of the hydrogen from the methyl group attached to the benzene ring to the ether oxygen, giving rise to the peak at m/z 118. The corresponding loss was not observed in the fragmentation of 2 Γ·. This was attributable to a greater electronegativity of the fluorine atom than that of a hydrogen atom.
In the fragmentations of the compounds studied here, the so-called ortho-effect is operative. During the fragmentation of 2 +. and 4 Γ·, interesting F atom rearrangements were observed.