Estimation of Hammett sigma constants from calculated atomic charges using partial least squares regression

Hammett constants describe the electronic donating or withdrawing capabilities of a given substituent. Since Hammett constants represent information of an electronic nature, their values are to be linked with atomic charges and orbital-derived parameters of the atoms of the substrate bearing the substituent. A series of 132 para- and meta-substituted benzoic acid structures has been built and energy minimized using MOPAC/AM1. Atomic charges and frontier orbital coefficients of the benzoic moiety have been calculated. These parameters were highly interrelated. Using partial least squares regression, we showed that Hammett constants can be satisfactorily estimated from these electronic parameters.