Kinetic studies of cis-trans isomerization of stilbene anion radicals with a quantitative-electrolysis ESR method

The isomerization of the anion radical (CS^•-) of cis-stilbene (CS) is studied by means of a quantitative-electrolysis ESR method. The progress of the isomerization from CS^•- to the anion radical (TS^•-) of the trans isomer (TS) was successfully monitored by taking advantage of the difference in the spectral extension between the ESR spectra of two isomers. From these kinetic data, it is concluded that the isomerization of CS^•- proceeds through CS^2- and that the rate-determining step is the disproportionation of CS^•-s. Since the present isomerization proceeds in the absence of chemical reductants or alkali-metal cations, it can be regarded as the isomerization of CS^•- itself which has not been studied so far.