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

The molecular vibrations of the title compound (DHBP) were investigated by IR polarization spectroscopy on samples partially aligned in stretched poly ethylene (PE) and correlated with those of the closely related compound ant hralin (1,8-dihydroxy-9(10H)-anthracenone). Compared to the case of anthral in, the-analysis of the observed linear dichroism (LD) for DHBP is complica ted by lower molecular symmetry and by less efficient alignment in stretche d PE, but approximate vibrational transition moment directions could be der ived for about 27 vibrational transitions. The molecular geometry and norma l vibrational modes were calculated by ab initio Hartree-Fock (HF) theory a nd by various density functional theories (DFT). As in the case of anthrali n, vibrational motions associated with the carbonyl and hydroxy groups coup le strongly with CC and CH motions, resulting in the prediction of a very c omplex IR spectrum. Excellent consistency with observed transitions was obt ained with DFT, particularly with the B3LYP functional, while corresponding HF results were much less satisfactory, partly because of failure to descr ibe the intramolecular H-bonding prevailing in DHBP. (C) 1999 Elsevier Scie nce B.V. All rights reserved.