Substituent Effect on the Acidity Strength of para-C6H4XB(OH)2 Boronic Acid: A Theoretical Investigation

Abstract

The para-substituent effect on the acidity strength of boronic acid (para-C6H4XB(OH)2; X = NMe2, NH2, OMe, H, F, Cl, CHO, COOH, NO2) is explored at the B3LYP*/6-31+G(d, p) level of theory in an aqueous solution. The conductor-like polarized continuum model (CPCM) is used for the calculation in the aqueous phase. The CPCM calculations are performed with the SMD-Coulomb atomic radii. Then, the pKa values corresponding to these molecules are calculated in an aqueous solution. Atomic charges of the acidic proton are calculated with QTAIM, APT, and Mulliken methods. A linear correlation between the calculated pKa values with the Hammett constant, deprotonating energy, and atomic charges of acidic proton are analyzed.