Perturbation theory of substituent effect. Quantum chemical estimation of the Hammet ρ constants

Abstract

Based upon a simple model describing the substituent effect only by a change in the Coulombic integral Δαμ, a relation is derived which can be viewed as a quantum chemical analogue of the Hammet equation. This relation and knowledge of the reaction constant ρ for a reaction on a skeleton chosen as a standard make it possible to predict theoretically the magnitude of the ρ constant for this reaction on an arbitrary conjugated skeleton provided that for the latter the Hammet equation holds.