The KBM equation for determining solvent frequency shifts is generally useless for predicting <i>v</i>C=O frequencies for compounds in various solvent systems. The <i>v</i>C=O frequencies for acetone and tetramethylurea in various solvents do not correlate with dielectric effects (ε) of the solvent. A series of factors most likely determine the extent of solute/solvent-induced vibrational mode frequency shifts.
R. A. Nyquist, "The KBM Equation for Solvent-Induced Frequency Shifts Revisited," Appl. Spectrosc. 43, 1208-1211 (1989)