Transition state ion pair

Figure 9. Schematic representation of upper portion of potential eneigy surface for merging of substitution mechanisms. A Sjsj 1 mechanism. No nucleophilic solvation in transition state ion pair intermediate (possibly nudeophilically solvated) B Sn2 (intermediate). Transition state is nudeophilically solvated by solvent (SOH) intermediate is a nudeophilically solvated ion pair (see Fig. 8) C Classical Sn2. No energy minimum. In curves A and B, the second transition state may be of higher energy than the first in cases where internal return is important.

Figure 11 Potential of mean force for a model ion pair in a dipolar solvent. Also shown are the configuration of the nearest-neighbor solvent molecules for several of the important ion pair configurations contact ion pair, transition state ion pair, and solvent-separated ion pair. Adapted from ref. 130.

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