Substituent effects on the intramolecular hydrogen bond in 1-hydroxyanthraquinone: AIM and NBO analyses

The substituent effects on the intramolecular hydrogen bond in 1-hydroxyanthraquinone were investigated within the framework of the atoms in molecules theory and using natural bond orbital analysis. The calculated results show that introducing a substituent at the ortho- or meta-position has different effects: the substituents at ortho-position strengthen the intramolecular hydrogen bond, while the effects of the meta-position substituents are minor. Both ortho- and meta-position electron-donating substituents increase the covalent nature of the intramolecular hydrogen bond, whereas the meta-position electron-withdrawing substituents decrease it. Furthermore, striking parallels were found between the geometries, binding energies, and topological properties of the complexes studied. The topological properties of the bond critical point and ring critical point, the delocalization index DI(O, H), and the integrated properties of the interatomic surface delta(O, H) can all be treated as indicators to measure the strength of the intramolecular hydrogen bond.