DFT Study of Complexation Reactions Involving Dicarboxylic Acids: Hydrogen Bonds, Influence of Solvent Nature

Abstract

Quantum chemical studies of the protolytic ability of some dicarboxylic acids are carried out. The geometric and kinetic parameters of the dimeric molecules of maleic, succinic, tartaric, oxalic, and adipic acids are in-vestigated. The dimerization energies of these substances are determined by considering the basis set super-position error (BSSE). The effect of the presence of a carbon skeleton, unsaturated bonds, and hydroxy sub-stituents on the dicarboxylic acids kinetic parameters is confirmed. The frontier molecular orbitals of the studied dimeric acids molecules are considered and the HOMO-LUMO energy gap is determined. The ob-tained values of the energy gaps show an increase in the stability of a number of cyclic compounds formed by the participation of two hydrogen bonds. The ability of the acids to form complexes with the 3,6-di-tert-butyl-2-hydroxyphenoxyl semiquinone radical is studied. The effect of the nature of the solvent on the activation barrier of the complexation reaction of the semiquinone radical — dicarboxylic acid system is analyzed using the CPCM and IEFPCM models. The dependence of the energy parameter on the solvent polarity is estab-lished using the examples of toluene, tetrahydrofuran, and nitrobenzene. The DFT method at the B3LYP lev-el, together with the 6-31+G (d, p) basis set, is used to optimize molecular structures. The calculations are carried out using the Gaussian 16 Revision A.03 WIN64.