The mass spectra of mixed tetraalkyltins are described and analysed. The fragmentation pattern is in agreement with the hypothesis of prefered Sn(1V) and Sn(I1) valence states in the tin-containing fragments. These states are reached by losing an alkyl radical from the next higher unfavourable valence state, o r by losing an alkene or alkane molecule from a favourable valence state. The ease of cleavage of a carbon-tin bond in the molecular ion parallels the stabilization of the leaving alkyl radical by hyperconjugation. The findings are tentatively extrapolated to the general behaviour of tetraalkyl derivatives of group IV organornetallics.The electron impact fragmentation of symmetrical tetraalkyltins has been described recently by Occolowitz [l]. Apart from this work, only publications relating the mass spectra of tetramethyltin We wish to report now the mass spectra of some symmetrical and mixed tetraalkyltins.The principal ions observed are listed in The results given in tables I and VI show that the mass spectra of alkyltrimethyltins are not very different from one another and the following general description of the fragmentation patterns can be given.The molecular ion RSnMe,+ is generally not very intense (1% or less, see table VI) and is even less important than in the case of aryltrimethyltins [Ill, [12]. The ion resulting from the loss of CH,. is more abundant and reaches 16%, excepted for (*) -Part V: Gielen, M. and Nasielski, J., Bull. Soc. Chim. Belg., 77 (1968) 5.
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