Reparametrization and/or Determination of Hammett, Inductive, Mesomeric and AISE Substituent Constants for Five Substituents: N+(CH3)3, CH2N+(CH3)3, CH2Py+, CH2SO2CH3 and PO(OCH3)2

Abstract

Ten meta- and para-substituted benzoic acids with substituents N+(CH3)3, CH2N+(CH3)3, CH2Py+, CH2SO2CH3 and PO(OCH3)2 were synthesized. Dissociation constants of these acids were determined in five solvents (water, ethanol, methanol, N,N-dimethylformamide, dimethyl sulfoxide) at 25 °C. Dissociation constants of benzoic acid derivatives with other substituents H, CH3, NHCOCH3, OCH3, F, Cl, Br, I, COCH3, CN, NO2, SO2CH3 were taken from the literature (calibration set). Substituent constants σm, σp, σI, σR, and σi for substituents N+(CH3)3, CH2N+(CH3)3, CH2Py+, CH2SO2CH3, and PO(OCH3)2 were calculated by nonlinear and PLS (partial least-square method with latent variables) calibration in three correlation models using the calibration set. Nonlinear regression appears more suitable and more universal than PLS calibration. The advantage of nonlinear regression is its independence on possibly missing data in the given solvent, evaluation of precision (standard deviation), the accessibility of necessary software, and easy calculation. However, in contrast to PLS calibration, this procedure fails in calculation of substituent constants with description of properties of substituents (substituent constants σI, σR). The obtained values of substituent constants are in good agreement with those published in the literature.