Solvent nucleophilicity and definition of the nucleophilic constant

Winstein, Fainberg and Grunwald, later expanded eqs. (1.11.8) and (1.11.9), taking into account the nucleophilicity of solvents, which obviously exerts influence upon reaction rates. They derived eq. (1.11.10)  

There are other expressions that correlate ionizing power and nucleo-phylicity, e.g., that of Swain, Mosely and Brown, but it appears that eq. (1.11.10) is the most frequently used one.  

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