CONFORMATIONAL EFFECTS ON THE ELECTRONIC-STRUCTURE AND CHEMICAL-REACTIVITY OF LIGNIN MODEL P-QUINONE METHIDES AND BENZYL CATIONS

The electronic structure and its dependence on the conformation in typ ical lignin model intermediates, beta-aryletheric p-quinone methide th oxyphenoxy)]propylidene-2,5-cyclohexadien-1-one} and related benzyl ca tion has been determined on the basis of semi-empirical quantum chemic al calculations. Electrostatic but not frontier orbital characteristic s of lignin intermediates were demonstrated to be dependent on the con formation. Conformationally induced electrostatic non-equivalence of t wo possible routes of nucleophile approach to the reaction center may be the main cause of stereoselectivity of the reactions of quinone met hides (but not related cations) with nucleophiles. Quinone methides an d related cations also differ in their intramolecular charge transfer properties.