Intermolecular GB catalysis

FIGURE 2.5 Plots of vs. total buffer concentration of GB ([Buf].j.) at a constant pH and different total concentrations of nucleophile ([HNuJ = A, B, C, D, and E where A B C D E), which represent the experimental validity of Equation 2.47. 

Pseudo-first-order rate constants (k s) for the reaction of A-ethoxycarbon-ylphthalimide (53) with A-methylhydroxylamine (CH3NHOH) in the buffer solutions of CH3NHOH of constant pH follow the kinetic relationship  

The rate of hydrolysis of A-(4-nitrobenzoyl)pyrrole has been found to be sensitive to GB catalysis. In addition, carbonyl- 0 exchange kinetics have also been carried out at a single pH (9.48) as a function of DABCO buffer concentration. At 

The occurrence of efficient intermolecular GB catalysis has been reported in the intramolecular nucleophiUc reactions of the neutral trifluoroethyl 2-aminom-ethylbenzoate. The rate-determining step in the GB catalyzed reaction involves proton transfer in concert with leaving-group departure. 

The kinetic term kg,[GB][HNu][Sub] shonld also be rednced to k[GB][Sub] in the rate law even if the nucleophilic reaction between HNn and Snb occurs in or before the rate-determining step provided [HNn]/[GB] 100 and [GB]/[Sub] 100 under the reaction conditions of the rate stndy. Thns, under such reaction conditions, k = kgb[HNu], and this relationship cannot be verified 

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The realization of the occurrence of intermolecular GA catalysis comes from the experimental fact of the presence of a kinetic term kgJBH+][NuH][Sub] (where BH+ is the GA, NuH is the nucleophile, and Sub is the substrate) in the rate law for the nucleophilic reaction between NuH and Sub in the presence of BH+. But this kinetic term is kinetically indistinguishable from kinetic term k[H+][B][NuH][Sub], which represents SA-GB catalysis or SA-nucleophilic catalysis. However, these kinetically indistinguishable catalytic mechanisms can be resolved, at least qualitatively, as described in the following text. 

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