CONFORMATIONAL EFFECTS IN BETA-FUNCTIONAL ACYCLIC ORGANOSILICON COMPOUNDS

A detailed analysis has been carried out of the proton magnetic resona nce (PMR) splitting patterns of the methylene absorptions of beta-chlo roethyltrimethylsilane at 298 K. The effects of temperature on the PMR spectra of this compound have been examined. In addition, the PMR spe ctra of beta-hydroxyethyltrimethylsilane, beta-methoxyethyltrimethylsi lane, and beta-bromoethyltriphenylsilane were obtained at a number of temperatures. A theoretical analysis of the PMR spectrum of beta-chlor oethyltrimethylsilane shows that the splitting patterns of the methyle ne absorptions may be satisfactorily represented by a hindered AA'XX' system of protons. Commercial molecular modelling software has been us ed to investigate the effects of van der Waals interactions on the con formations of some of these molecules. It is concluded from these vari ous observations that there is severe steric hindrance about the C-C b ond 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 kinet ic effects observed in such systems.