Solvent effects and steric course in the Solvolysis of 1,3,3-trimethyl-2-exocyclepentyl mesylate in comparison with 1,1,3,3-tetramethyl-2-exobutyl system

The rates of solvolysis in various solvents were determined for 1,1,3,3-tet ramethyl-2-oxobutyl tosylate (1OTs) and 1,3,3-trimethyl-2-oxocyclopentyl me sylate (4OMs). The rate data for 1OTs reinforced that the linear Grunwald-W instein (GW) relationship of 1OMs previously reported by Creary for non-aqu eous solvents must also hold for aqueous organic solvents. 4OMs showed a ma rkedly dispersed GW relationship that is, on the other hand, well correlate d with an extended GW equation involving a nucleophilicity parameter. Such solvent dependence, such marked effects of added sodium azide on rates, and the 100% inversion of configuration of the solvolysis product showed that the solvolysis of 4OMs would be categorized to S(N)2(intermediate), whereas 1OMs and 1OTs solvolyze via limiting S(N)1. The negligible susceptibility of 1OTs toward nucleophilicity of solvent and azide probe indicates that th e nucleofuge leaves along the C=O axis in such a manner that the back-strai n (B-strain) in the ground state is efficiently relieved in the transition state. Comparison of solvolysis rates of 1OMs and 4OMs with those of the co rresponding parent substrates suggests that the transition states of these substrates would not be stabilized by carbonyl pi conjugation. The origin o f the unexpectedly fast rates of solvolysis of 1OMs has been discussed.