In the presence of a three-component catalyst (tri-n-butylamine, tetramethyl-ethylenediamine, and cuprous chloride), the addition reaction of a series of silanes (trichlorosilane, phenyldichlorosilane, methyldichlorosilane, diphenylchlorosilane, methylphenylchlorosilane, diphenylchlorosilane, methylphenylchlorosilane, diethylchlorosilane and, triethylsilane) with acrylonitrile has been studied.Under the same reaction conditions, a quantitative tomparison of the reactivities of these silanes revealed that the percentages of yields for the addition give a "sigmoid" curve when plotted versus the corresponding inductive indices for the substituted atoms or groups in the silane molecules.