Conformation, hydrogen bonding and UV solvatochromic shifts of benzophenones in primary alcohols

摘要

Solvent effects on structural properties of benzophenones have been investigated by means of UV spectroscopy and the AM1 method. In primary alcohols, the compounds exhibit conformers with non-planar structures. Unsubstituted benzophenone only presents flexible symmetrical conformations while o-hydroxy-benzophenones also possess two non-symmetrical conformers in equilibrium. The dipolar moments of the compounds were predicted by relating properties of the symmetrical conformers with solvatation parameters of the alcohols. The percentage of non-symmetrical conformers, which lack the intramolecular hydrogen bonding, ranges between 1 and 2.5. On the other hand, results matching those stated above were obtained by studying the strength of this bond under the assumption of the occurrence of an intramolecular proton-transfer reaction. The UV solvato-chromic shifts recorded were satisfactorily correlated with the calculated absorption frequencies. It was concluded that the magnitude of the analyzed properties are determined by the degree of occurrence of solute-solvent interactions, which essentially depend on the polarity, polarizability and hydrogen bond donating ability of the primary alcohols.