EVIDENCE FOR SIGMA-PI INTERACTION IN SOME ALLYLTIN COMPOUNDS - UV PHOTOELECTRON-SPECTROSCOPY AND LCBO CALCULATIONS

A series of allyltin compounds, R3-nClnSnCH2CH=CH2 (R = Me, n-Bu; n = 0-2) and Ph3SnCH2CH=CH2, have been studied by gas-phase UV photoelectron spectroscopy, in order to determine the extent, if any, of σ-π conjugation (hyper-conjugation) between the σ(SnCH2) bond and the π(CC) orbital of the allyl group. Analysis of the spectra, supported by a fragment analysis based on LCBO (Linear Combination of Bond Orbitals) calculations, indicated that the hyperconjugation operates for all the members of the series, the extent decreasing on passing from R = Me to R = n-Bu and, within each series, with increasing n.