2,2'-dihydroxybenzophenone (DHBP) contains similar bifold intramolecular H-bonding as the psoriatic drug anthralin, but because of steric interference the phenolic rings are twisted in a propeller-like manner, resulting in a molecular structure of C2 symmetry. In contrast to the case of C2v anthralin, the description of the vibrational structure of the compound is thus complicated by the circumstance that moment directions for transitions polarized perpendicular to the C2 axis (z) are not uniquely determined by symmetry, but can take any direction in the xy plane. The molecular vibrations of DHBP were investigated by IR polarization spectroscopy on samples aligned in stretched polyethylene. The observed Linear Dichroic (LD) absorbance curves, corresponding to absorbance measured with the electric vector of the sample beam parallel (U) and perpendicular (V) to the stretching direction, were analyzed by the stepwise reduction procedure, and in spite of relatively poor alignment, approximate orientation factors K could be determined for 27 vibrational transitions. On the basis of the polarization data and with the help of theoretical predictions it was possible to assign the most important fundamentals observed in the IR spectra. Theoretical predictions at the HF/6-31G* level did not lead to satisfactory agreement with the observed transitions, but the results obtained with B3LYP/6-31G* was in excellent consistency with the general appearance of the observed spectra.
|Tidsskrift||Polarization Spectroscopy of Ordered Systems - PSOS|
|Status||Udgivet - 1999|