Solvation energy changes

Hence, the solvation energy change accompanying the disproportionation can compensate the repulsion term. In weakly solvating media, association with counter ions occurs and the disproportionation equilibrium should be considered, for example, as follows ... 

Thus in the case that BH+ is H30+, Equation (14) becomes an identity reaction, for which there is no medium effect, and m =0. On the other hand, if BH+ is a protonated aniline, m = 1. These values provide fixed points on a scale of solvation energy changes associated with proton transfer between H30+ and the protonated base under study. 

As noted above, nonlocal dielectric theory provides the starting point for continuum approaches to SD. The derivation given below follows that presented by Song et al. [47], The solvation energy change due to solute electronic transition occurring at t = 0 is given by... 

Current opinions concerning ion-pair modelling share wide consensus on the electrostatic description of the pairing interaction (even if the appropriate values of a and R are still debated), but call attention to the repulsion at r < a, and to the importance of free solvation energy change and other short-term interactions. 

Dynamics In light of the encouraging results for absolute solvation energies and equilibria, applications of continuum solvation models to the dynamics of organic reactions also are expected to be very fruitful. Ionic reactions (e.g., the classical S[s 2 mechanism) may proceed in qualitatively different ways in solution and in the gas phase, and continuum solvation models provide a convenient and economical way to map out solvation energy changes as a function of the reaction coordinate. 

Figure 3. Dependence on basicity of the rate constants for the reactions of phenoxide, alkoxide, and hydroxide ions with p-nitrophenyl thioacetate. The solid line for phenoxide ions (circles) has a least-squares slope of Pnuc = 0.68, and a dotted line of slope 0.17 has been drawn through the points for ethoxide and trifluoroethoxide anions (triangles). The dashed line shows the expected rate constants if the full solvation energy change for phenolate ionization is added to AG (see the text). (Reproduced from reference 25.

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