Alkyl substituent effects. Part 1. An analysis of alkyl inductive properties in terms of group connectivity

Abstract

Formulae are derived which express the scales of the inductive substituent constants σ_I and σ*, the group electronegativities χ_R, and the polarisability constants P of alkyl groups in terms of base-constants and ‘connectivity characteristics,’ pure numbers the value of which depend only on the number of carbon atoms a group contains and the pattern of their bonding. The formulae are of predictive value in calculating σ_I, σ*, χ_R, or P for any alkyl group and in discerning what these scale of measurement have in common and where they differ. It is shown that alkyl σ* is not a artefact as has been claimed, that σ_I and σ* are linear functions of alkyl group electronegativity, and that P probably has a hyperconjugative element.