Computational evaluation of σI and σR substituent constants

A computational approach for the evaluation of σI and σR substituent constants is outlined. It is based on correlations between theoretically evaluated electrostatic potential at nuclei (EPN) values for the carbon atoms (VC) in substituted benzene and bicyclo[2,2,2]octane derivatives containing the same polar group at position 1. Theoretical computations at B3LYP/6-311+G(2d,2p) level were performed. Quite satisfactory correlations linking σI and σR constants and quantities derived from the respective VC values in the two series of molecules were obtained. The obtained equations provide a simple and meaningful approach for theoretical evaluation of σI and σR constants. The method is applicable also to polysubstituted and polynuclear aromatic hydrocarbons.