Hydrogen-Bond Donicity in DMSO and Gas Phase and Its Dependence on Brønsted Acidity

The hydrogen-bond (HB) donicity of various HB donors, expressed as standard Gibbs free energy of HB formation with chloride ion, was studied experimentally in dimethyl sulfoxide (DMSO) and computationally in DMSO and the gas phase. Acidity and HB donicity data in the gas phase and DMSO have been obtained for 77 HB donors from different compound families. Applicability of two computational methods (SMD and COSMO-RS) for calculation of solvation contribution to reaction free energy in DMSO was evaluated and discussed. The quality of calculated Gibbs free energies of solvation was assessed using the correlation between HB strengths in solvent and in the gas phase. The investigation of the relationships between HB donicity and Brønsted acidity showed that in the gas phase the correlation is good, and within structurally uniform compound groups both acidity and donicity are described well by substituent constants. The same correlation in DMSO is less distinct. Bidentate HB donors are characterized by higher HB donicity than could be expected from their acidity in both media, and therefore, these HB donors have an important advantage in anion binding applications, e.g., in catalysis