SOLVENT EFFECTS ON CHEMICAL PROCESSES .7. QUANTITATIVE DESCRIPTION OF THE COMPOSITION DEPENDENCE OF THE SOLVENT POLARITY MEASURE E(T)(30) IN BINARY AQUEOUS-ORGANIC SOLVENT MIXTURES

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 x(2), 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.