Electron paramagnetic resonance study of silacyclohexyl and 1-methylsilacyclohexyl radicals

Abstract

Silacyclohexyl and 1-methylsilacyclohexyl radicals have been studied in adamantane matrices from –86° to room temperature. The preferred conformation for silacyclohexyl and the exclusive conformation for 1-methylsilacyclohexyl is the chair form with the SOMO on silicon equatorial. Long-range couplings to the equatorial γ-C—H protons are observed. For silacyclohexyl, a small proportion of the conformer with the SOMO axial is observed at –86°, giving rise to a substantial coupling to the axial β-C—H protons. At room temperature, equilibration of the two conformers is relatively fast, giving rise to averaged spectra. From the EPR spectra of silacyclopentyl and silacyclohexyl radicals, the dependence of β-C—H coupling constants on the dihedral angle with the SOMO on silicon is shown to have a double-maximum form with a maximum value at 180° and a smaller maximum at 0°.