Hammett’s seminal work demonstrated a linear relationship between reaction rates or equilibrium constants and Hammett sigma values. Still today, the Hammett plot is a valuable tool that reveals useful inferences about transition states. As such, the Hammett sigma value for hundreds of common substituent constants have been reported. Interestingly, despite the utility of organoboron compounds in catalysis, targeted synthesis, and pharmaceutical industries, the Hammett sigma value for common boryl substituents have yet to be measured. Using benzoic acid as the parent compound, Hammett sigma values of common boryl substituents can be readily calculated by the difference in pKa of the substituted and unsubstituted benzoic acid. Herein, we present efforts toward measuring boryl substituent effects, which include the synthesis of desired boryl compounds and the pKa measurements of those substituted compounds via potentiometric titrations and UV-Vis spectrophotometric methods.

Determining Hammett sigma values for common boryl substituents by potentiometric and UV-Vis titrations

ACS Spring 2022

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