Variation in the correlations obtained between electron acceptor number (AN) values for each solvent versus the <i>v</i>C=O frequencies for acetone and tetramethylurea in solution with these solvents suggests that the AN values are not a precise measure of solute/solvent interaction for all solute/solvent systems. Factors such as intermolecular hydrogen bonding between solute and solvent and the differences between molecular geometry of the solutes and solvents most likely account for differences in the solute/solvent interaction for different solutes in the same solvents.
R. A. Nyquist, T. M. Kirchner, and H. A. Fouchea, "Vibrational Frequency Shifts of the Carbonyl Stretching Mode Induced by Solvents: Acetone," Appl. Spectrosc. 43, 1053-1055 (1989)