Photohydration of Styrenes and Phenylacetylenes. General Acid Catalysis and Broensted Relationship

Article abstract of DOI:10.1021/ja00253a035

The acid-catalyzed photohydration of a series of substituted styrenes and phenylacetylenes have been investigated in aqueous buffer solutions.General acid catalysis was clearly detected in five cases with a range of catalysts, and approximately linear Broensted plots gave α values in the range 0.14-0.18.The rate enhancements caused by excitation from S₀ to S₁ were estimated from comparisons with thermal hydration data to be in the 1E11-1E15 range.Treatment of the dependence of the rate constants for general acid catalysis (k_HA) on the buffer pK_HA values with multiple regression analysis suggests that the Broensted plots are smoothly curved, as predicted by Eigen and by the Marcus equation.However, reliable values of the Broensted curvature could not be established.The possible catalytic reactivity analogous triplet states was examined with a series of nitrosubstituted analogues, but no general acid catalysis could be detected.The factors controlling the detection of general acid catalysis in these photoreactions are discussed.