Anchimeric assistance, and

To limit the scope of this review and to reduce overlap with other reviews, some related topics will only be discussed briefly. The addition of salts can affect both the rate and the course of solvolytic reactions and provides very important evidence for ion-pair intermediates. A full discussion of this topic has been published recently (Raber etal., 1974) additional comments are given onpp. 27,32. Also, we have generally excluded solvolyses known to proceed by competitive nucleophilically solvent-assisted and anchimerically assisted pathways. These solvolyses are very common (e.g. even n-propyl tosylate yields 87% of rearranged product during trifluoroacetolysis Reich et al., 1969), but a detailed account has been published recently (Harris, 1974). Recognition that solvolytic reactions could proceed by these two competitive, assisted pathways provided the key to the solution of the controversial phenonium ion problem (Lancelot et al., 1972 Brown et al., 1970), as well as inspiring the reinvestigation of the mechanisms of solvolyses of simple secondary substrates discussed in Section 2. 

The development of quantitative scales of solvent nucleophilicity based on solvolysis reactions is reviewed. Effects of solvent nucleophilicity are illustrated by product studies, by correlations of kinetic data, and by quantitative estimates of competing nucleophilic pathways, including competing solvent-assisted and anchimerically assisted pathways. The problem of separating quantitatively the nucleophilic and electrophilic solvent contributions to reactivity is discussed. Recent results on the nucleophilicities of aqueous sulfuric acid mixtures are presented. 

Solvent Effects on Competing Nucleophilically Solvent Assisted (ks) and Anchimerically Assisted (JtA) Processes. Schleyer et al.s work (8) on solvolyses of 2-adamantyl (II) arose from earlier studies (71) of the competition between ks and fcA processes in (3-arylalkyl systems (XII and XIII). Apparently, no crossover occurred between the two processes, because rate-product correlations were observed. Hence, any cationic intermediates in the ks process must be sufficiently strongly solvated to prevent attack by... 

Scheme 7. Armed-Disarmed ects and anchimeric assistance.

Figure 1. Armed-Disarmed effects and anchimeric assistance.

When the bridging ring is somewhat larger the inward rotation of the bridgehead H-atoms becomes sterically feasible, and anchimerically assisted ionization for the exo-halide becomes available. Thus, solvolysis of the exobromide (8) gives rrflfw-cyclo-oct-l-en-3-ol (Equation 6.5). 

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