CONFORMATIONAL EFFECTS IN BETA-FUNCTIONAL ACYCLIC ORGANOSILICON COMPOUNDS

A detailed analysis has been carried out of the proton magnetic resonance (PMR) splitting patterns of the methylene absorptions of beta-chloroethyltrimethylsilane at 298 K. The effects of temperature on the PMR spectra of this compound have been examined. In addition, the PMR spectra of beta-hydroxyethyltrimethylsilane, beta-methoxyethyltrimethylsilane, and beta-bromoethyltriphenylsilane were obtained at a number of temperatures. A theoretical analysis of the PMR spectrum of beta-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 beta-halo systems. For the related beta-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.