CNDO Calculation of Dipole Moment Derivatives and Infrared Intensities of C6H6 and C6F6

The dipole moment derivatives of C₆H₆ and C₆F₆ have been calculated using the complete neglect of differential overlap (CNDO) approximate molecular orbital theory. The calculated set of derivatives with respect to the symmetry coordinates ${\mathrm{(\partial \; p/\partial \; S}}_j)$ for the e_1u species of C₆H₆ agrees remarkably well with the unique experimental set of derivatives determined from infrared intensity measurements and the normal coordinate analysis for C₆H₆ and its deuterated analogues. The success of the benzene calculation suggests that we may have confidence in the CNDO results for C₆F₆, even though the agreement with the experimental results is much worse. An analysis of the ${\mathrm{\partial \; p/\partial \; S}}_j$ values is given in terms of bond moment derivatives. The failure of the CNDO theory to predict a sufficiently large ``rehybridization moment'' to explain the observed intensity difference between in‐plane and out‐of‐plane bending vibrations is discussed.