Employment of quantum chemical descriptors for Hammett constants: Revision Suggested for the acetoxy substituent

The Hammett para constant ( σ p ) of the acetoxy group has been estimated by applying widely available quantum chemical descriptors, such as NPA charges, Wiberg bond indices, electron densities at bond critical points, as well as electrostatic potential at nuclei. The revised σ p value is predicted to be in the range of [−0.08, −0.02]. Direct evaluation of proton transfer free energies between the substituted benzoic acids and the benzoate anion by employing the SMD solvation model resulted in a reasonable linear correlation with the Hammett constants with a prediction of σ p = −0.02 for the OAc group.