Yukawa-Tsuno model

The greater than unit value of Kf in pure solvents is the result expected by the field effect model (33) on a distance basis. The lower than unit value ofKj in the mixed aqueous organic solvents appears to be related to preferential hydration of the reaction center, which results in an increased effective dielectric constant from the m- compared to the p- position. The fact that values fall into two separate categories for pure organic and mixed aqueous organic solvents does not support the treatments of Exner (20) or Yukawa and Tsuno (16). 

An alternative diparametric model was proposed by Yukawa and Tsuno for use with electron-deficient active sites and was originally written as equation 6 ... 

The addition of extra terms will naturally improve a correlation and the a and correlations essentially do this for reactions with a resonance component. The simple approach neglects the possibility that the resonance and inductive transmissions may differ in model and reaction in question. Yukawa and Tsuno [48] proposed a correlation where p and p (Eqn. 60) are essentially measures of transmission of substituent effects by induction and resonance. 

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