Kinetics of reactions of ethyl-and phenylmagnesium chlorides with chlorosilanes, RMeSiCl2, were investigated in diethyl ether under pseudo-first order conditions with a great excess of the Grignard reagent. Rate constants for alkyl substituted silanes correlate well with Es (Si) steric parameters. A good linear correlation of rate data for substituted phenyl derivates with σ0 inductive constants together with correlations of the literature data rule out the ...