A generalized relationship, which includes contributions of the s-characters of C=O bond and the net atomic charges, is employed to elucidate C=O bond stretching vibrational frequencies based on the maximum bond order hybrid orbital calculations at ab initio HF/6-31G* level of theory. It is demonstrated that the change of the s-characters is the most important factor for determining the change of C=O stretching frequencies. The C=O stretching frequencies calculated by using the explicit relationship obtained are in good agreement with the corresponding experim...
