Pulse radiolysis of benzoquinone and hydroquinone. Semiquinone formation by water elimination from trihydroxy-cyclohexadienyl radicals

A number of transient free-radical spectra produced during the pulse radiolysis of benzoquinone, and hydroquinone, have been observed and characterized. The semiquinone radical and radical-anion are produced directly by reactions of e–aq and H atoms with benzoquinone and also by the unimolecular elimination of water from trihydroxycyclohexadienyl radicals. The latter species arise directly by OH addition to hydroquinone. The extinction coefficients of the various species and the reaction rate constants for their formation and decay have been measured. The equilibrium constant for the benzsemiquinone radical and radical-anion equilibrium is 10–4 M.