Photochemistry of 4‑Chlorophenol in Liquid and Frozen Aqueous Media Studied by Chemical, Compound-Specific Isotope, and DFT Analyses

The photochemistry of 4-chlorophenol in liquid and frozen aqueous solutions and on the surface of ice grains yields substantially different photoproducts. Several complementary experimental and theoretical methods, such as trace analyses of the photoproducts, trapping experiments, compound-specific isotope analyses, and quantum chemical calculations, were used to study the reaction mechanism differences. A similar carbon kinetic isotope effect determined for the photolysis of 4-chlorophenol samples in the temperature range of 20 to −40 °C and the results of trapping experiments suggest that heterogeneous cleavage of the C–Cl bond in the excited state is probably a common key step that leads to the formation of carbene and hydroxyphenyl cation intermediates. We conclude that the subsequent specific reactions of these species under various conditions are responsible for the formation of different final photoproducts