Knowledge Bank

Blanchette, Mast and $King1$ have shown that characteristic effective charges’’ for the carbon and hydrogen atoms can be calculated for hydrocarbons simply from a knowledge of the intensity sum for 2 isotopic derivatives of any hydrocarbon. Since these effective charges’’ are independent of the normal coordinates, they are especially important in testing the quality of quantum-mechanical wavefunctions with respect to their ability to predict infrared intensities. Although the approximate quantum-mechanical wavefunctions generated by the CNDO technique are not expected to give the best possible predictions for these quantities, the general success of these wavefunctions in correlating infrared intensities $results2$ has encouraged us to calculate effective charges from these wavefunctions. The results from these calculations indicate that the empirically discovered constancy of these parameters in hydrocarbons may indeed be justified by the calculated results. The calculated results provide some insight into the nature of these parameters. We are grateful to the National Science Foundation (Grant No. GP-17818) for support of this work.