Uranyl Photochemistry with Alkenes:  Distinguishing between H-Atom Abstraction and Electron Transfer

We have studied the quenching of the uranyl ion in aqueous acetonitrile with a series of alkenes. The quenching rate constant (kq) increases linearly with decreasing ionization potential (IP) for a series of hexene isomers, as seen in a plot of ln(kq) vs IP; no correlation is observed between the quenching rate and the bond dissociation energy of the allylic C−H bond. These results demonstrate that the mechanism of quenching for alkenes is electron transfer from the alkene to uranyl.