Low-Temperature Electrochemistry III. Application to the Study of Radical Ion Decay Mechanisms

The ability of low-temperature techniques to isolate the primary one-electron transfer oxidation or reduction process with a cryoquench of the coupled chemical reactions responsible for the radical ion decay mechanism is demonstrated. Successful cryoquenching, producing radical ion lifetimes of at least 2 sec, was achieved for: a radical anion fragmentation decay reaction (reduction of o- and p-iodonitrobenzene in dimethylformamide); a radical cation dimerization reaction (oxidation of triphenylamine in butyronitrile); a radical cation scavenging reaction by nucleophilic solvent impurity (oxidation of 1,2,3,6,7,8-hexahydropyrene in butyronitrile); and a radical cation scavenging reaction by nucleophilic solvent (oxidation of 9,10-diphenylanthracene in dimethylformamide). In contrast, the lifetime of the 9,10-dimethylanthracene cation radical in butyronitrile is less at low temperatures; the decay reaction involves a prior equilibrium reaction of the cation radical (DMA) with another cation radical (DMA) or with parent (DMA) and represents a case where new information has been provided by the low-temperature technique.