46278-25-5Relevant articles and documents
Concerted Acetyl Group Transfer between Substituted Phenolate Ion Nucleophiles: Variation of Transition-State Structure as a Function of Substituent
Ba-Saif, Salem,Luthra, Ajay K.,Williams, Andrew
, p. 2647 - 2652 (1989)
Second-order rate constants (kArO) have been measured for the concerted displacement of aryl oxide from aryl acetates in aqueous solution by substituted phenoxide ions.Values of kArO obey linear Bronsted correlations when either the leaving group or the attacking phenolate ion structures are varied.The Bronsted coefficients obey the equations βnuc = 0.20pK1g - 0.68 and β1g = 0.15pKnuc - 1.73 to a good degree of precision, and the variation indicates that the structure of the transition-state changes within the range of phenolate ions studied; this alsoprovides confirmation that a concerted mechanism operates.The equations for βnuc and β1g predict the equation (log kii = 0.17pKa2 - 2.41pKa + C) for kii, the rate constant for the reaction of aryl oxide ion with acetates bearing identical aryl oxide leaving groups.The identity rate constants may be interpolated from the observed rate constants (kArO) and exhibit excellent fit to the above equation with the single disposable parameter, C, set at 6.5.This is the first report of curvature in a Bronsted plot of identity rate constants.Effective charge development and loss on leaving and attacking oxyanions is fully balanced in the transition state when entering and leaving nucleophiles have a pKa of 7.1.Tetrahedral or acylium ion-like transition-state structures are predicted for hypothetical phenols with pKa's of 11.7 and 2.0, respectively.
