Molecular and vibrational structure of 2,2′-dihydroxybenzophenone: infrared linear dichroism and quantum chemical calculations

Abstract

The molecular vibrations of the title compound (DHBP) were investigated by IR polarization spectroscopy on samples partially aligned in stretched polyethylene (PE) and correlated with those of the closely related compound anthralin (1,8-dihydroxy-9(10H)-anthracenone). Compared to the case of anthralin, the analysis of the observed linear dichroism (LD) for DHBP is complicated by lower molecular symmetry and by less efficient alignment in stretched PE, but approximate vibrational transition moment directions could be derived for about 27 vibrational transitions. The molecular geometry and normal vibrational modes were calculated by ab initio Hartree–Fock (HF) theory and by various density functional theories (DFT). As in the case of anthralin, vibrational motions associated with the carbonyl and hydroxy groups couple strongly with CC and CH motions, resulting in the prediction of a very complex IR spectrum. Excellent consistency with observed transitions was obtained with DFT, particularly with the B3LYP functional, while corresponding HF results were much less satisfactory, partly because of failure to describe the intramolecular H-bonding prevailing in DHBP.