Ab initio study of flavonoids

Flavone and the flavylium ion have been studied at the Hartree–Fock, Møller–Plesset, and B3LYP hybrid density functional level to determine the structure and barriers to internal rotation. Both molecules have a high perpendicular barrier about the single bond connecting the phenyl ring with the benzpyrone and benzopyrylium ring, respectively. In contrast to biphenyl, both molecules have low coplanar barriers. B3LYP overestimates the perpendicular barrier heights compared to the other methods. The dependence of the population and orbital energies on the torsion has been investigated and the structures of both flavonoids have been compared with monohydroxy derivatives. Solvent effects on the barriers have been estimated by means of a reaction field model.