Empirical Parameters of Solvent Polarity from other Measurements

The general SPP scale of solvent dipolarity/polarizability and the specific SB and SA scales of solvent HBA basicity and HBD acidity, respectively, are orthogonal to one another and they can be used in the correlation analysis of solvent effects in single- or, in combination with the others, in two- or three-parameter correlation equations, depending on the solvent-influenced process under consideration see also Section 7.7. Examples of the correlation analysis of a variety of other solvent-dependent processes by means of SPP, SB, and SA values, including those used for the introduction of other solvent polarity parameters, can be found in references [335-337, 340-342]. In particular, comparisons with Kamlet and Taft s n scale [340] and Winstein and Grunwald s Y scale [341] have been made. 

5 Empirical Parameters of Solvent Polarity from Other Measurements 

An important measure of the total molecular cohesion per unit volume of liquid is the cohesive pressure c (also called cohesive energy density), which characterizes the energy associated with all the intermolecular solvent/solvent interactions in a mole of the solvent. The cohesive pressure is defined as the molar energy of vapourization to a gas at zero pressure, Af/y, per molar volume of the solvent, V, according to Eqs. (3-5) and (5-76) in Sections 3.2 and 5.4.2, respectively [93, 94]. The cohesive pressure c is related to the internal pressure n cf. Eq. (3-6) and Table 3-2 in Section 3.2. 

Sometimes, Hildebrand s solubility parameter 8 has been incorrectly used in linear Gibbs energy relationships cf. for example [96, 97, 226, 255]. Since in linear Gibbs energy relationships the correlated solvent-dependent solute properties e.g. Ig K, Ig k, h v) are proportional to Gibbs energy changes of reaction or activation (AG, AG ) and 

It has been shown that gas-Hquid chromatographic methods are particularly suitable for a quantitative characterization of the polarity of solvents. In gas-liquid chromatography it is possible to determine the solvent power of the stationary liquid phase very accurately for a large number of substances [98, 99, 259, 260]. Many groups of substances exhibit a certain dependence of their relative retention parameters on the solvation characteristics of the stationary phase or of the separable components. In determining universal gas-chromatographic characteristics, the so-called retention index, I, introduced by Kovats [100], is frequently used. The elution maxima of individual members of the homologous series of n-alkanes (C H2 +2) form the fixed points of the system of retention indices. The retention index is defined by means of Eq. (7-41), 

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