In this paper,a method for the systematic and quantitative evaluation of the inducfive effect exerted over a certain chemical bond in the molecule by a group,from the electronegativities and the atomic radii of its constituent elements,has been presented.The constant for the inductive effect of the group thus obtained is designated as the inductive effect index of the group.It has been found that for a given reaction,the energy changes,the logarithms of the equilibrium constants,and the logarithms of the rate constants can be expressed,respectively,as linear functions of the corresponding inductive effect index involved in the reaction,and that the percentages of chemical changes in the reaction,such as percent yield and conversion,give "sigmoid" curves when plotted versus the latter.These linear functions and sigmoid curves constitute a general quantitative relationship between molecular stmcture and chemical reactivity.