Catalysis, general base diffusion limit

General base catalysis of the cyclization of ethyl 2-hydroxymethyl 4 nitrobenzoate [35], where the acyl group is further activated by electron withdrawal by the nitro-substituent, is characterized by a Bronsted coefficient of 0 97, i.e. unity within the limits of error, suggesting that proton transfer is a diffusion-controlled process (Fife... 

In this last example an even greater curvature is apparent if we include catalysis by the species H2O and H30. The same is true for a number of other reactions, and also for base catalysis by H2O and OH , even when the rates of both the forward and reverse reactions are far below the diffusion-controlled limit. It is doubtful, however, how far general conclusions can be drawn from curvature based only on reaction with solvent... 

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