Grunwald-Winstein equation limitations

The success of the single parameter Grunwald-Winstein equation is largely due to the limited range of solvent change such as variation of composition of mixtures. When different solvent types are employed extra terms are needed in the equation to fit the data. Solvolysis reactions in aliphatic nucleophilic substitution involve nucleophilic attack of the solvent and it is unlikely that solvents of different structure would have similar nucleophilicities excepting those in a series of mixed solvents such as ethanol-water (Chapter 2). The simplest treatment involves dividing the solvent action into nucleophilic and electrophilic components as shown in Equation (32). 

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