Abstract Simple potential model relations for experimental carbon 1s ionization energies (EC,1s) and carbon mean dipole moment derivatives ( p C ) obtained from experimentally measured infrared fundamental band intensities are investigated for a diverse group of 29 molecules. Positive and negative correlations of the EC,1s values and neighboring atom electrostatic potential contributions, V, with the p C values result in large variances for the EC,1s–V values and excellent potential model fits. MP2/6-311++G(3d,3p) level Koopmans’ energies are shown to provide the most precise potential model fits with correlation coefficients of 0.9996, 0.9962 and 0.9960 for sp3, sp2 and sp hybridized carbon atoms, respectively. Potential models using experimental ionization energies adjusted by HF/6-31G(d,p) level relaxation energies are almost as precise. The slopes of the potential lines obtained using Koopmans’ energies or experimental ionization energies adjusted by relaxation energies increase with increasing values of the inverse covalent sp3, sp2 and sp radii. Relative electrostatic potentials at carbon nuclei calculated directly from electronic densities of MP2/6-311++G(3d,3p) molecular orbital wave functions are shown to be in good agreement with those estimated by mean dipole moment derivatives calculated from the same wave functions.