Ab initio study of the intramolecular proton transfer in dihydroxyanthraquinones

An ab initio study of 1,4-, 1,5- and 1,8-dihydroxyanthraquinone was conducted using the Hartree-Fock method with the 3-21G and 6-31G** basis sets. The three compounds exhibit two intramolecular hydrogen bonds; this enables an intramolecular proton transfer that can take place in a concerted manner or in two steps in the former two. All the minima and saddle points corresponding to the potential intramolecular proton transfer processes were identified. In addition, the geometry of the absolute minimum of each compound was consistent with experimental data. The strength of the hydrogen bond was assessed and the bond was found to be quite strong and markedly additive in nature despite the substantial stiffness of the molecules Studied. (C) 2001 Elsevier Science B.V. All rights reserved.