Application of Mechanistic and Transition-State Indicators to endo and exo-2-Norbornyl Arenesulfonates. Definition of a new Mechanistic Indicator

Article abstract of DOI:10.1021/jo00236a029

We have mechanistically classified endo- and exo-2-norbornyl arenesulfonates by using two common probes: the effect on rate of added thiourea and rate correlation in aqueous ethanol and trifluoroethanol.Interestingly, the exo isomer is improperly classified by each of these probes because of medium-dependent ion-pair return.In search of better mechanistic indicators, pseudo-first-order solvolytic rates and products have been determined for a series of endo- and exo-2-norbornyl arenesulfonates.Using these and literature data, we have compared these substrates with others by plotting α-deuterium isotope effects against β_1g^Me values determined for a series or arenesulfonates in the same or a similar solvent.The use of this type of plot as a heuristic method for distinguishing k₈ and k_Δ substrates is discussed.Finally, our product studies are consistent with the involvement of solvent-seperated ion pairs in the solvolysis of 2-norbornyl arenesulfonates.Different alcohol-ether product ratios for the isomeric esters in consistent with dual pathways for product formation with the endo substrates.