Solvent Equations Based on Macroscopic Quantities

The Swain Equation (34) provides very accurate predictive power for a limited range of solvents and processes based on a statistical analysis of a five-parameter equation. The origins of the Swain parameters are not explicit, although the acity (A) and basity (B) coefficients are related to electrophilic and nucleophilic processes respectively. Many fundamental processes have been implicated in solvent effects and the equation of Koppel and Palm (Equation 37) incorporates the major factors thought to be involved. 

The exponents g, p, c and b are parameters of the reaction or process being affected by change in solvent. The term f( ) is a function of the dielectric constant, usually (e - 1)/(2b + 1), is a refractive index 

Taft advanced Equation (39), analogous to that of Kopple and Palm, where ti is an average solvation parameter obtained from solvato-chromic shifts and a is a hydrogen-bond acidity scale. 

Abraham et al., Solvent Effects in Organic Chemistry - Recent Developments, Can. J. Chem., 1988, 66, 2673. 

Abraham, Scales of Solute Hydrogen-bonding Their Construction and Application to Physicochemical and Biochemical Processes, Chem. Soc. Rev., 1993, 73. 

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