Relations between acceptor numbers of Lewis acids and OH vibrations

It is found that the increase of the solvent effect on vibration spectra of OH groups induced by Lewis acids is linear proportional to the Gutmann acceptor numbers AN. This gives a simple method of AN determination by OH vibration frequencies and of the understanding of these numbers. The ANs are not only useful for a common characterization of solvent effects, but for complex formations, too. The significance of the AN values, determined by different methods, and of other methods to characterize solvents effects by one single number and the influence of Lewis acids are discussed.