Knowledge Bank

Ultraviolet photolysis of condensed-phase acetyl chloride $(CH3COCl)$ produces ketene $(H2C=C=O)$ and HCl in a 1:1 dimer complex. The reaction mechanism sharply differs from the photodissociation of gas-phase molecules which produces chlorine and acetyl radical $(CH3CO)$ that further dissociates to $CH3$ and CO. Two mechanisms of photodissociation of condensed-phase acetyl chloride have been proposed; concerted elimination and the caged abstraction. Thermodynamic analysis, polarized IR studies, and gencral spectroscopic observations of the photoproducts are use to show that the photodissociation of condensed acetyl chloride follows a concerted elimination mechanism.