Transition-State Variation in the Solvolysis of Cyclopentyl para-Substituted Benzenesulfonates

摘要

Rate constants for solvolyses of cyclopentyl para-substituted benzenesulfonates are reported for aqueous binary mixtures with acetone, ethanol and methanol. These data are interpreted using the equations of original and extended Grunwald-Winstein relationship, Hammett equation, potential energy surface model, and quantum mechanical model. The Grunwald-Winstein plots of first-order rate constants for cyclopentyl benzenesulfonates with YOTs (based on 2-adamantyl tosylate) show a dispersion phenomenon while the extended Grunwald-Winstein plots show a good correlation (r > 0.997) for the solvolyses of cyclopentyl tosylate, benzensulfonate, and para-chlorobenzenesulfonate. This study has shown that (i) the magnitudes of m, l and m/l associated with a change of solvent composition indicate a relatively advanced bond-breaking in the transition state for the solvolysis of cyclopentyl tosylate, (ii) the decrease of ヱL value with solvent change from pure ethanol to pure water implies a product-like transition state, where bond breaking is much more progressed than bond formation (iii) both the potential energy surface and quantum mechanical models are applicable for the prediction of the transition state variation involving more product-like SN2 transition state, and (iv) the SN2 reaction via product-like transition state appears to cause the dispersions in the original Grunwald-Winstein correlations.