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 pK_a 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 pK_a values with the Hammett constant, deprotonating energy, and atomic charges of acidic proton are analyzed.