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Abstract: 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 (V C) 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 V C 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. [Copyright &y& Elsevier]

Abstract: Density functional theory computations at the B3LYP/6-311+G(2d,2p) level for a series of 25 para-subsituted phenoxide ions were performed in analyzing the intramolecular effects determining the σ − reactivity constants for aromatic systems. Very good linear relationships were established between the electrostatic potential at nuclei values, NBO and Hirshfeld atomic charges at the phenoxide oxygen in p-substituted phenolates and the σ − constants. Comparisons of the charge shifts induced by polar groups at para position in the phenoxides and in substituted at position 4 bicyclo[2.2.2]octan-1-olates reveals that very strong conjugative effects determine the high values of σ − constants for electron-withdrawing substituents. Inversely, low charge transfer between substituents and the negatively charged reaction center in the case of electron donating groups is in harmony with the low values for the σ − constants for such moieties. The unusual resonance interactions between substituents and the negatively charged reaction center were quantitatively assessed. [Copyright &y& Elsevier]