Correlaiton of Hammett σ constants withNMR parameters for substituted phenylsilanes, phenylmethylsilanes and phenyldimethylsilanes

Abstract

The 29Si-H coupling constants and SiH chemical shifts have been determined for a series of substituted phenylsilanes, phenylmethylsilanes and phenyldimethylsilanes. Excellent correlations with almost identical ϱ values, were found to exist between the coupling constants and the Hammett σ constants of the ring substituents for the three series. Treatment of the couplings withing the framework of the Hammett-Taft equation gave new Taft σ * constants for six substituted phenyl groups. The SiH chemical shifts were found to be much less sensitive to change in structure than J-( 29Si-H). The 13C-H coupling constants and chemical shifts of the methyl groups of substituted phenylmethylsilanes and phenyldimethylsilanes have also been measured and correlated by the Hammett σ constants. The ϱ values obtained are compared with those of substituted phenyltrimethylsialnes reported by other workers.