Interplay of Intramolecular Hydrogen Bonds, OH Orientations, and Symmetry Factors in the Stabilization of Polyhydroxybenzenes

Polyhydroxybenzenes are the parent compounds of large classes of derivatives, many of which exhibit biological activities. The study of derivatives highlights the importance of the conformation stabilizing factors of the parent compounds. To identify these factors, a systematic comparative study of polyhydroxybenzenes was carried out through a computational study of all possible structures and conformers in vacuo and in three solvents differing by their polarities and by the types of interactions with the solute molecule (water, chloroform, and acetonitrile); the results in solution are complemented by the study of adducts with explicit water molecules and, for the simpler structures, also with explicit acetonitrile molecules. The greatest conformation stabilizing effect pertains to intramolecular hydrogen bonds, with preference for consecutive H-bonds. Uniform orientation of the phenol OH is a stabilizing factor for structures with meta OH groups. Preference for structures with meta OH and with greater symmetry increases as the medium polarity increases. The coexistence of intramolecular H-bonds and solute-solvent intermolecular H-bonds in water and acetonitrile solution narrows the solvent-effect difference between conformers with and without intramolecular H-bonds. Comparison of results from different calculation methods (HF, MP2, and DFT/B3LYP, with 6-31G(d,p) and 6-31++G(d, p) basis sets) shows consistency of the identified trends. (C) 2010 Wiley Periodicals, Inc. Int J Quantum Chem 111: 3701-3716, 2011