Solvation effects electrophilic contributions

Separation of Nucleophilic and Electrophilic Contributions to Solvation Effects. The discussion on the appropriate choice of m value for the N0Ts scale (equation 7) is part of a more general problem of dissecting the nucleophilic contributions (corresponding to the IN term in equation 5) and electrophilic contributions (included in the mY term in equation 5) to solvent effects. When a substrate reacts by a nucleophilically solvent assisted pathway, m decreases and l increases, often in a uniform manner (equation 12). Schadt et al. proposed (3) that an increase in nucleophilic assistance (increase in l) caused delocalization of positive charge, which led to a decrease in m. All of the deviations from the rates expected for SN1 (kc) reactivity were attributed to nucleophilic solvent assistance (3) Schadt et al. (3) assumed that m values for kc processes would be the same as for 2-adamantyl (II), and more recent data for 1-adamantyl (I), 1-adamantylmethylcarbinyl, and 1-bicyclo[2.2.2]octyl tosylates support this assumption (4, 53). 

For the analysis of SN1 solvolyses, Abraham et al. (9) have proposed an equation (equation 3) based on sensitivities toward solvatochromatic properties. In equation 3, tr is a measure of solvent dipolarity-polarization, a is a measure of solvent hydrogen bond donor acidity, and P is a measure of solvent hydrogen bond acceptor basicity. More recently, a term governing cavity effects has been added, and this term is considered to represent an important contribution (10, 11). The cavity term can be directly related to the square of the Hildebrand solubility parameter (10-12). A similar analysis by Koppel and Palm (13, 14) involves terms governed by solvent polarity, solvent polarizability, electrophilic solvation ability, and nucleophilic solvation ability. Recently, a cavity term has also been added to this analysis (12). 

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