Electronegativity of ionic groups. Evaluation from MNDO calculations

Abstract

The electronegativities (χ_G) of some 78 groups/atoms(G) including some 11 ionic ones have been evaluated from the charge on the H atom in the corresponding H−G molecules. The charges are determined by the MNDO method of Dewar at the optimised geometries. For some 38 molecules/ions whereab initio molecular orbital calculations are available, a reasonable linearity (correlation coefficientr=0·900) has been observed between the MNDO charges and the charges obtained at the 6–31G ^*//6–31G ^* level. The very good linear correlation (r=0·950) obtained between the χ_G values and Inamoto’s i scale for some 72 groups/atoms including some 8 monocationic groups shows that the method works quite well for the monocationic groups. However the anionic groups probably cannot be tackled in the present approach. The¹ J _cc (ortho-ipso) coupling constants in mono-substituted benzenes also correlate linearly with the χ_G values for some 33 groups/atoms to a satisfactory extent (r=0·917). It is mentioned that there does not exist a proper theoretical scale for group electronegativity which can accommodate ionic and neutral groups on a uniform basis.