Electronic charge distribution and moments of five- and six-membered heterocycles

Abstract

Using ab initio wave functions and the full operators, dipole and second moments are reported for a number of five- and six-membered ring heterocycles containing the elements nitrogen, oxygen, sulphur, and phosphorus. The agreement with experiment is satisfactory and a linear relationship µ_exptl.= 0·952µ_calc. is obtained with an average error of 0·29 D. With the exception of the quadrupole moments, the second moments are just outside the experimental error in the worst cases. Population analyses for the compounds are found to be additive in bond contributions, and this assists in the interpretation of the σ- and π-dipole moments. The difference in average position between the valency shell π-electrons has been related to aromatic character.