Influence of solvents on the conformation of benzoin

The conformation of benzoin in several organic solvents is investigated by infrared spectrometry and dipolometry. The frequencies, intensities, and band shapes of the ν(OH), ν(CO), and aromatic ring vibrations indicate that in solvents of low proton acceptor ability, the cis conformer with intramolecular OH···O hydrogen bonding is preserved. In solvents of large proton acceptor ability there is equilibrium between the cis and trans conformers. The dipole moments are less sensitive to conformational changes, but indicate the same trends. The results are discussed as a function of the specific solvation of the O atoms or OH groups of benzoin.