Solvent effects on chemical processes. Part 7. Quantitative description of the composition dependence of the solvent polarity measure ET(30) in binary aqueous–organic solvent mixtures

Abstract

The solvation effect component of the phenomenological model of solvent effects is applied to E_T(30), the molar transition energy of the Dimroth–Reichardt betaine, in binary aqueous–organic solvents. The dependence of E_T(30) on x₂, the mole fraction of organic cosolvent, can be quantitatively described for all 17 systems studied. New data are given for 9 of these systems. It is found that a 1-parameter model suffices to describe the composition dependence of the highly polar cosolvents, whereas a 2-parameter model is needed to account for other cosolvents, which yield a nonhyperbolic composition dependence. The solvation parameters, which are exchange equilibrium constants, yield correlations suggesting their positive dependence on cosolvent hydrophobicity and electron-pair donor ability.