Correlations Br0nsted plots

A linear Br0nsted plot thus implies a linear correlation of kinetic and thermodynamic quantities. The constant A is evidently equal to the activation free energy for a reaction in the same series having = 0, so in place of A we shall write AGq. We... 

A recent study of the reactions of 2,4-dinitrochlorobenzene and of picryl chloride with a series of nucleophiles that are presented in Table 6 shows that a plot (not shown) of log k against the pK values of all the nucleophiles is badly scattered77. Differences of up to 108 are observed for bases with similar pKa values. Part of this scatter is due to deviations that result because different families of nucleophiles (with different nucleophilic atoms) give rise to different Br0nsted correlation lines. Thus, for the reactions of picryl chloride good correlations are observed for a family of oxyanions (ft = 0.38, plot not shown), primary and secondary amines (Figure 4, ft = 0.52) and quinuclidines (Figure 4, P = 0.66). 

As in the case of Br0nsted correlations, one can expect different quantitative behaviour in plots of this kind when the type of substrate and the base used is varied. It can readily be shown that superposition of all currently available data leads to large scatter in... 

A number of studies of the acid-catalyzed mechanisms of enolization have been done. We can consider cyclohexanone as a typical case. The reaction is catalyzed by various carboxylic acids and substituted ammonium salts. The effectiveness of the various acids as catalysts correlates with their pKa values. When plotted according to the Br0nsted catalysis law, the value of the slope a is 0.74. When deuterium or tritium is introduced in the a position, there is a marked decrease in the rate of acid-catalyzed enolization /ch/ d 5. This isotope effect indicates that the C-H bond cleavage is part of the rate-determining step. The generally accepted mechanism for acid-catalyzed enolization pictures the rate-determining step as deprotonation of the protonated ketone ... 

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