Short and long range contributions to the inductive effect in π electron systems

Abstract

It is shown that the inductive effect of a substituent can have contributions of both exchange and Coulomb type, but that the exchange terms can be treated empirically as though they arise from a short-range field effect. Calculations of the exchange terms for the halogens and the methyl group are in accord with the empirical values of inductive parameters deduced from spectroscopy. Evidence is given that for a methyl group the inductive perturbation is almost entirely of short range type and is probably dominated by the exchange terms but for a chloro substituent both the short range exchange repulsion and the long range Coulomb attraction are important.