Solvent effect on the conformation of Benzil

The conformation of benzil is investigated by PM3 and density functional th eory (B3LYP) combined with the 6-31G(d,p) basis set. The variation of the r elative energy with the O=C-C=O torsion angle indicates only one rather fla t minimum, reflecting the flexibility of the benzil molecule. The dipole mo ment is measured in several organic solvents of various polarity and the IR and Raman spectra investigated in the C=O stretching region in the same so lvents. The torsional O=C-C=O angle is evaluated from the dipolar and vibra tional data. The results indicate that, in all the solvents, benzil is in a skewed conformation, the cisoid conformation being slightly favoured when the polarity of the solvent increases. The contribution of electrostatic an d specific interactions to the reduction of the torsional angle is discusse d. (C) 2001 Elsevier Science B.V. All rights reserved.