Electron paramagnetic resonance study on some alkylsilane radical cations in γ-irradiated CF3CCl3 matrices

Abstract

Radical cations of ethyl-, propyl-, butyl-, ethylmethyl-, propylmethyl- and diethyl-silanes in CF₃CCI₃ matrices at 77 K give two-line EPR spectra with separations of around 6 mT, independently of chain lengths and silicon positions. From results on some deuteriated alkylsilanes, and with INDO–MO calculations, it is concluded that each of the two-line spectra is attributable to the hyperfine coupling of the β-trans proton (β-H_trans) with respect to the slightly elongated α-carbon-silicon (C_α–Si) bond, where an unpaired electron is mainly confined. The anti configuration of the Si–C_α–C_β–H,_trans bond sequence is caused by maximization of the hyperconjugative effect between the unpaired electron localized in the C_α–Si bond and the C_β–H_trans, bond.