Fragmentation and isomerization of ionized trimethylphosphine sulfide (CH3)(3)P(S): ion structures and ab initio MO calculations

EI fragmentation of trimethylphosphine sulfide (CH3)(3)P(S) (1) is reported and discussed. [1](+.) mainly retains the connectivity of the neutral mole cule and no rearrangements to other long-lived isomeric farms occur. Howeve r, some [1](+.) ions undergo a unimolecular reaction by a [1,3]-hydrogen sh ift from carbon to sulfur atom to produce the short-lived carbon centered y lide radical [(CH3)(2)((CH2)-C-.)P+-SH]. Further, isomerization of the mole cular ion by an [1,2]-shift of a methyl group from phosphorus to sulfur is suggested which leads to [(CH,),P-SCH3](+.). Compared to [1](+.) the coordi nation number at phosphorus in the latter ion is reduced from four to three . Structures of fragment ions [C-2,H-6,P,S](+) (m/z 93), [C-3,H-8,P](+) (m/ z 75) and [C-2,H-6,P](+) (m/z 61) have been examined by collisional activat ion (CA) mass spectrometry. All. the even-electron ions exist with a phosph onium structure as dimethylthioxophosphonium- [(CH3)(2)P = S](+) (m/z 93), dimethyl-methylenephosphonium-[(CH3)(2)P = CH2](+) (m/z 75), and methyl-met hylenephosphonium-ion [(CH3)HP = CH2](+) (m/z 61), respectively. The experi mental findings are confirmed and complemented by the results of ab initio MO calculations. Copyright (C) 1999 John Whey & Sons, Ltd.