The solvent effects on the solvolysis of threo-2-aryl-1-methylpropyl p-toluenesulfonates were analyzed with the aid of the extended Winstein–Grunwald Equation. The aryl-assisted kΔ solvolysis of 2-(p-methoxyphenyl)-1-methylpropyl and 2-methyl-2-phenylpropyl p-toluenesulfonates failed to give a single linear correlation with the YOTs parameter. The dispersion against YOTs cannot be due to nucleophilic solvent assistance. The m values from the plots of 2-(p-methoxyphenyl)-1-methylpropyl and 2-methyl-2-phenylpropyl p-toluenesulfonates against YOTs were significantly lower than m = 1.0 for the limiting kc solvolysis. Significantly improved correlations (R > 0.99; SD < 0.14) were obtained for the p-methoxy, 3-chloro-4-methoxy, and p-methyl derivatives with the YΔ scale based on the solvolysis of 2-(p-methoxyphenyl)-2-methylpropyl p-toluenesulfonate, instead of with YOTs. No improvement by the YΔ treatment was obtained for the unsubstituted compound (R = 0.97; SD = 0.22). A new similarity comparison analysis in terms of YOTs and YΔ, i.e., log (k/k80E) = mcYOTs + mΔYΔ, was applied successfully to the present kΔ solvolyses. The degree of YΔ character relative to the YOTs one, scaled by mΔ/(mc + mΔ), varies for 1-methyl-2-phenylpropyl tosylates in the range from 1.0 to 0.00 in the consistent manner expected if the dispersion in the YOTs plot becomes less pronounced for solvolyses of less significant anchimeric assistance. There is a continuous spectrum of behavior between the extreme pure kc mechanism and the extreme pure kΔ one.

The solvolysis rates of (1-arylcyclobutyl)methyl and (1-arylcyclopropyl)methyl p-toluenesulfonates were measured in a wide variety of solvents. The aryl-assisted kΔ solvolysis of [1-(p-methoxyphenyl)cyclobutyl]methyl p-toluenesulfonate did not give a linear Winstein–Grunwald correlation using the 2-adamantyl-based YOTs scale, but did show dispersion for different binary solvent mixtures. An extended dual-parameter treatment, log (k/k80E) = mcYOTs + mΔYΔ, successfully correlated the present set of kΔ solvolyses with R > 0.995 and SD < 0.09. The blending parameter MΔ (= 0.51mΔ/(mc + 0.51mΔ)) increases monotonically with increased electron donation by the substituent, showing an increased dispersion of the YOTs plot with increasing anchimeric assistance. The solvolysis of (1-arylcycloalkyl)methyl p-toluenesulfonates demonstrates the varying extent of anchimeric assistance by the neighboring groups, from a completely synchronous aryl-assisted process for the p-methoxy derivative of (1-phenylcyclobutyl)methyl p-toluenesulfonate, via moderately to weakly aryl-assistance by the p-methyl derivative and the unsubstituted compound, to a completely aryl-unassisted kc process for the more electron-withdrawing aryl derivatives and the (1-arylcyclopropyl)methyl p-toluenesulfonates. The dual-parameter equation enables one to monitor the varying extent of anchimeric assistance in the transition state. From the results we propose a general solvolysis framework involving a continuous spectrum of kc − kΔ mechanisms for anchimerically assisted solvolysis.

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