Electronic structure of ring and chain substituted styrenes and their reactivities in the reaction with peroxyl radicals

Abstract

The structure–reactivity relationship in the chain propagation step of radical chain oxidation of styrenes substituted in the ring (ortho, meta and para) and in the vinyl group (position α and β), the addition of a peroxyl radical to the double bond, was investigated. With the PM3 quantum chemical methods the electronic structure of the reactants, transition state (TS) and the enthalpy of reaction (ΔH_R^add) were calculated. A linear correlation between ionisation potentials and energies of the HOMO was observed. The calculated bond lengths and charges on atoms at the reaction centre in the TS in comparison to their reactant values and also the negative ΔH_R^add show that the TS is early and charge transfer from molecule to radical dominates in the TS. For styrenes a three parameter correlation of the addition rate constants (k) with the reaction enthalpy, E_HOMO and coefficient C₁ at the p_z atomic orbital of the HOMO of the attacked carbon atom was obtained.