Communication: Infrared spectroscopy of protonated allyl-trimethylsilane: Evidence for the β-silyl effect

beta-trimethylsilyl-2-propyl cation has been formed by the gas phase protonation of allyltrimethylsilane and characterized by infrared multiple photon dissociation spectroscopy. The experimental C-beta-C-alpha(+) stretching feature at 1586 cm(-1), remarkably blue-shifted with respect to a C-C single bond stretching mode, is indicative of high double bond character, a signature of beta-stabilizing effect due to hyperconjugation of the trimethylsilyl group in the beta-position with respect to the positively charged carbon. Density functional theory calculations at the B3LYP/6-311++G(2df,2p) level yield the optimized geometries and IR spectra for candidate isomeric cations and for neutral and charged reference species. (C) 2013 AIP Publishing LLC.