Thomas-Reiche-Khun populations in X-CH3 and X-C2H5 series of molecules

Calculations of nuclear electric shieldings, equivalent to dipole moment geometric derivatives, and related to atomic polar tensors, are presented for X-CH3 and X-C2H5 molecules with X = NH2, OH and F. The electric shielding tensors satisfy a constraint for the electrostatic equilibrium, i.e., the mixed length-acceleration Thomas-Reiche-Khun sum rule, which gives important indications on the reliability of theoretical predictions of IR intensities and leads to the definition of atomic populations. Numerical evidence was found for the additivity and transferability of atomic populations, within the X-substituted alkane series.