Studies on labile chargetransfer complexes between o-chloranil and a series of phenols

The electron donor-acceptor (EDA) interactions between o-chloranil and a series of phenols have been studied in dioxan medium. Except for resorcinol, the EDA complexes are formed instantaneously on mixing the donor and the acceptor solutions and then they decay slowly into secondary products. In case of resorcinol, formation and decay of the EDA complex are slow and simultaneous. The kinetics of all these reactions have been studied spectrophotometrically and the formation constants of EDA complexes have been determined from kinetic data. The hv(CT) values change systematically as the number and position of the -OH groups change in the aromatic ring of the phenol moiety. From the trends in the hv(CT) values, the Huckel parameters (h((O) double over dot) and k(C-(O) double over dot)) for the -OH group, required for a PMO calculation on phenols, have been obtained in a straightforward way and the values so obtained, viz., 1.8 and 1.0 respectively, are close to the ones (1.8 and 0.8) recommended by Streitwieser on the basis of other evidences. (C) 1997 Elsevier Science B.V.