title: Reinterpretation of curved Hammett plots in reaction of nucleophiles with aryl benzoates: change in rate-determining step or mechanism versus ground-state stabilization.
abstract: A kinetic study is reported for the reaction of the anionic nucleophiles OH-, CN-, and N 3 - with aryl benzoates containing substituents on the benzoyl as well as the aryloxy moiety, in 80 mol % H2O - 20 mol % dimethyl sulfoxide at 25.0 degrees C. Hammett log k vs sigma plots for these systems are consistently nonlinear. However, a possible traditional explanation in terms of a mechanism involving a tetrahedral intermediate with curvature resulting from a change in rate-determining step is considered but rejected. The proposed explanation involves ground-state stabilization through resonance interaction between the benzoyl substituent and the electrophilic carbonyl center in the two-stage mechanism. Accordingly, the data are nicely accommodated on the basis of the Yukawa-Tsuno equation, which gives linear plots for all three nuceophiles. Literature reports of the mechanism of acyl transfer processes are reconsidered in this light.
authors.affiliation: Department of Chemistry, Ewha Womans University, Seoul 120-750, Korea. ihum@mm.ewha.ac.kr
authors.forename: Ik-Hwan
authors.initials: IH
authors.lastname: Um
authors.forename: Hyun-Joo
authors.initials: HJ
authors.lastname: Han
authors.forename: Jung-Ae
authors.initials: JA
authors.lastname: Ahn
authors.forename: Swan
authors.initials: S
authors.lastname: Kang
authors.forename: Erwin
authors.initials: E
authors.lastname: Buncel