METASTABLE ION STUDY OF ORGANOSILICON COMPOUNDS .10. O-CH3C6H4COOSI(CH3)(3) AND O-CF3C6H4COOSI(CH3)(3)

The unimolecular metastable ion dissociations of o-trimethylsilyl tolu ate, o-CH3C6H4COOSi(CH3)(3) (1) and its fluorine analogue, o-trimethyl silyl alpha,alpha,alpha-trifluorotoluate, o-CF3C6H4COOSi(CH3)(3) (2), upon electron impact, have been investigated by means of B/E linked sc an and high resolution data. The fragmentation processes of these comp ounds were elucidated with the aid of those of the corresponding acids , o-toluic acid, o-CH3C6H4COOH (3) and o-alpha,alpha,alpha-trifluoroto luic acid, o-CF3C6H4COOH (4), respectively. No molecular ion is observ ed for 2, but a fairly abundant molecular ion is observed for 1. The f ragmentation of 1(+.) is different from that of 2(+.), except for the loss of . CH3 from the respective molecular ions. In the case of 1, (C H3)(3)SiOH is eliminated from 1(+.) with the migration of the hydrogen from the methyl group attached to the benzene ring to the ether oxyge n, giving rise to the peak at m/z 118. The corresponding loss was not observed in the fragmentation of 2(+.). This was attributable to a gre ater electronegativity of the fluorine atom than that of a hydrogen at om. In the fragmentations of the compounds studied here, the so-called ortho-effect is operative. During the fragmentation of 2(+.) and 4(+. ), interesting F atom rearrangements were observed.