A Sum Rule For The Vibrational Intensities Of Substituted Methanes

An electronegativity model for the calculation of gas-phase fundamental intensity sums of the halomethanes is proposed. The substituent effective charges are assumed to be linearly related to their Mulliken electronegativities and the carbon effective charges to their average substituent electronegativities. The model is particularly convenient for analyzing atomic contributions to the intensity sums. The average absolute deviations of the intensity sums predicted by the model from the experimental sums are 27.0 km·mol-1 for eight training set molecules and 56.9 km·mol-1 for 24 test set molecules. These deviations are only 7.5% and 16.1% of their respective average experimental intensity sums. The model is also applied to the dihaloethylenes and the X2CY (X = F, Cl, Br; Y = O, S) molecules. © 1990 American Chemical Society.9451764176