METASTABLE ION STUDY OF ORGANOSILICON COMPOUNDS .9. CH3COOSI(CH3)(3) AND CF3COOSI(CH3)(3)

The unimolecular metastable dissociation of trimethylsilyl acetate, CH 3COOSi(CH3)(3) (1), and its fluorine analogue, trimethylsilyl trifluor oacetate, CF3COOSi(CH3)(3) (2), upon electron impact have been investi gated by means of a B/E linked scan, high resolution data, and D-label ing. The results are compared with those of the carbon analogue, tert- butyl acetate, CH3COOC(CH3)(3) (3). No molecular ion of any of these c ompounds can be observed, but loss of CH, occurs exclusively from the trimethylsilyl or tert-butyl groups. The fragmentation of 1(+.) is sli ghtly different from that of 3(+.), and quite different from that of 2 (+.). In the case of 3(+.), (CH3)(2)C=0 is eliminated from [3-CH3](+), giving rise to the peak at m/z 43, but the loss of (CH3)(2)Si=0 does not occur from [1-CH3](+). In the case of 2(+.), an interesting fluori ne atom (F) migration is observed.