SOLVENT EFFECTS ON CHEMICAL PROCESSES .7. QUANTITATIVE DESCRIPTION OFTHE 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 solven t effects is applied to E(T)(30), the molar transition energy of the D imroth-Reichardt betaine, In binary aqueous-organic solvents. The depe ndence of E(T)(30) on x(2), the mole fraction of organic cosolvent, ca n 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 su ffices to describe the composition dependence of the highly polar coso lvents, whereas a 2-parameter model is needed to account for other cos olvents, which yield a nonhyperbolic composition dependence. The solva tion parameters, which are exchange equilibrium constants, yield corre lations suggesting their positive dependence on cosolvent hydrophobici ty and electron-pair donor ability.