Conformational effects in β-functional acyclic organosilicon compounds

A detailed analysis has been carried out of the proton magnetic resonance (PMR) splitting patterns of the methylene absorptions of β-chloroethyltrimethylsilane at 298 K. The effects of temperature on the PMR spectra of this compound have been examined. In addition, the PMR spectra of β-hydroxyethyltrimethylsilane, β-methoxyethyltrimethylsilane, and β-bromoethyltrisphenylsilane were obtained at a number of temperatures. A theoretical analysis of the PMR spectrum of β-chloroethyltrimethylsilane shows that the splitting patterns of the methylene absorptions may be satisfactorily represented by a hindered AA′XX′ system of protons. Commercial molecular modelling, software has been used to investigate the effects of van der Waals interactions on the conformations of some of these molecules. It is concluded from these various observations that there is severe steric hindrance about the C–C bond of the ethyl moiety in the β-halo systems. For the related β-hydroxy and -methoxy systems the results suggest that the rotation of substituents about the C–C bond is significantly less hindered. These conformational preferences could account for certain steric and kinetic effects observed in such systems.