Physicochemical Properties and Structural Analysis of Some Organic Solvent (OS)- Water Systems: A Quantum Mechanical Study

Molecular interaction in organic solvents and water causes a significant change in physicochemical properties of organic solvent (OS)- water systems, which may also affect the stability of such systems. Although optimized models of OS-water systems have been shown to have strong hydrogen bond formation, some changes may occur in bond distances and angles following a molecular interaction between solvents and H2O or H3O+ ions. Organic solvents, such as aldehyde, ketone, carboxylic acid, amine, aniline, amide, etc., might have different interaction modes with water molecules, but the proton donor-acceptor nature of such systems greatly impacts their free energy, enthalpy, zero-point energy, and other thermodynamic parameters. The analysis of enthalpy changes (ΔHº) for all OS-water systems showed negative values, which reflects their exothermic behavior; however, the Gibbs free energy change (ΔGº) shows the feasibility of the formation of all types of OS-water systems. The hydrophobic or hydrophilic nature of such systems not only controls the stability of donoracceptor complexes but also defines their acidic or basic nature. In all cases, optimized models provide some detailed information about the changes in the geometry of OS-water mixtures. Furthermore, the physicochemical properties of OS-H3O+ and OS-H2O systems have been found to follow a similar trend. In this study, the standard free energy change (ΔGº), enthalpy change (ΔHº), zero-point energy change (ΔZPE), the effect of protonation, electron charge density, and other parameters of OS-H2O and OS-H3O+ systems were evaluated by quantum mechanical calculations.