Collect. Czech. Chem. Commun. 1989, 54, 136-150

New statistical parameters for description of solvent effect

Oldřich Pytela

Department of Organic Chemistry, Institute of Chemical Technology, 532 10 Pardubice


A new three-parameter statistical scale has been suggested to describe the solvent effect. The parameters were obtained by applying the method of conjugated deviations (suggested earlier by the author) to a set of 378 data series describing the solvent effect in various chemical and physical processes. The first parameter PA describes the solvent acidity in a medium of a given polarity, the second parameter PB predominantly reflects the solvent polarity with a contribution of basicity, and the third parameter PP refers to the polarity with a contribution of polarizability. The correlation equation, though additive by its form, is de facto an additive-multiplicative relation. Deviations of the parameters indicate a great variability of the solvent effect due to specific manifestations in particular systems. The correlations using the definition set of processes were most successful in the case of the data obtained from kinetic measurements and electronic and infrared spectra. Less significant correlations were obtained for the data from NMR and EPR spectroscopies and measurements of equilibrium constants. Distinctly worse results were found for other processes. The comparison with four most significant empirical equations applied to the same data was unambiguously in favour of the scale suggested (except for the interpretation of EPR data.