In this paper, we find that stretching vibration frequencies of the X=O for series of R1R2C=O, (RO)(2)CO, RCO2H, a-halogenated aldehydes, cross-RONO and R2NNO can be described by the ionicity indices of X and O atoms as follows: v = aINI((O))+bINI((X))+c, where a, b, c are regression constants, and INI(X), INI(O) represent the ionicity indices of X and O atoms. The efficiency of the model is verified by high correlation coefficients in the range of 0.960-1.000. Similarly, the ultraviolet absorption energy of ketones can also be characterized by the ionicity indices of C and O as Delta E = aINI...
