FRAGMENTATION REACTIONS OF THE TRIMETHYLSILYL ADDUCTS OF C-6 KETONES

The unimolecular (metastable ion) and collision-induced fragmentation reactions of the trimethylsilyl cation adducts of six C-6 ketones have been studied by tandem mass spectrometry. A major unimolecular fragme ntation channel involves regeneration of the trimethylsilyl cation; ot her fragmentation channels involve elimination of (CH3)(3)SiOH, C5H10, C4H8 and C3H6 from the adduct ions. Some mechanistic detail has been obtained from a study of the adducts with deuterium-containing ketones , and the reactions observed are compared with the fragmentation react ions of the protonated ketones. Collision-induced dissociation (CID) o f the adduct ion results in predominant formation of (CH3Si+. However, in the high energy (6 keV) CID new minor reaction channels, involving elimination of alkanes, CH4 to C4H10, become accessible. It is conclu ded that tandem mass spectrometry of the trimethylsilyl adducts provid es only limited ability to distinguish between isomeric ketones.