Fragmentation and rearrangement processes in the high resolution mass spectra of diphenylsilyl compounds

High resolution mass spectra of a series of diphenylsilyl compounds, Ph₂SiX₂(X=H, F, Cl) and Ph₂Si(oy)₂ (Y=Et, Me, H), were recorded. Results from selected metastable defocusing experiments showed that if X or OY can be readily lost stepwise, the relative abundance of the biphenyl radical rearrangement ion (d) is small; if neutral silicon species such as :SiX₂, SiX or :Si(OY)₂ are readily eliminated, the relative abundance of the ion d will be large. The ion d originates from both odd- and even-electron ions, thus making the radical site mechanism, which requires a phenyl radical to polarize the other phenyl group, rather unlikely to be an important general driving force. The condensation of phenyl groups could be more appropriately viewed in terms of bond liability and product stability. In the special case of diphenylsilyl catecholate, in addition to geminal cleavage of phenyl groups, complex fragmentation and rearrangement processes were also observed.