Characterization of Transition State based on Solvation Behavior

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The solvent effect on these solvolyses of aryl-assisted and benzylic solvolyses, despite the nucleophilically limiting nature, generally failed to give a single linear correlation with the Winstein-Grunwald Equation, using the adamantyl Y_<OTs> but showed characteristic dispersion for various binary aqueous solvent series. It is evident that developing charge at the reaction center in the transition state of benzylic k_c carbocationic process is highly delocalized through effective PI-overlapping with the aryl group, and this may cause a singificant loss of the highly oriented specific solvation at the charge-delocalized reaction center in comparison with that for aliphatic localized 2-adamantyl cation. The solvent polarity scale YDELTA based on p-methoxyneophyl solvolysis combined with the Y_<OTs> has shown a wide applicability to the solvolyses of benxylic arylalkyl tosylates involving varying degree of PI-delocalization interaction with the incipient carbocation charge ; log (k/k_O) = aY_<OTs> +bYDELTA. The equation can be applied to a series of aryl-assisted solvolyses in an extremely high precision, suggesting a continuous spectrum of k_c - kDELTA mechanisms. Benzylic k_c solvolyses can also be treated with linear combination of Y_<OTs> and YDELTA. Application of above generalized equation, including cN_<OTs> term, has also been extended to the nucleophilic solvent assisted solvolyses of alkyl and arylalkyl tosylates, e.g., for a series of substituted benzyl tosylates with limited success, particularly indicating no precise additivity (or non-linearity) for the nucleophilic solvent assistance.