A point-charge representation of nonbonding electron pairs: model derived from the ability of the hydrogen bond to act as a probe of electron density

A simple point-charge model is presented for some molecules B which assigns charges to atom centres and to nonbonding pairs, those for the latter placed at distances r along directions α as conventionally envisaged. The magnitude δ of the charge assigned to the nonbonding pairs is chosen so that the variation of the electrostatic interaction energy between B and HF with the angular position of HF agrees with that calculated on the basis of a more complete description (DMA) of the electrostatic charge distribution of B. The charges δ in the three molecules explored (B = H2O, H2CO, and H2S) prove to be only a few hundredths of an electron at distances r comparable with bond distances in B. Keywords: nonbonding pairs, point-charge model, hydrogen bond, Gillespie–Nyholm model, electron localization.