Duroquinone radical anion

Fig. 10-8 shows the observed CIDEP spectra for the reaction of triplet eosin Y (FlBr/ ) with duroquinone. In this figure, CIDEP spectra of the duroquinone radical anion were only observed. The spectra of Xn" were not observed because of its fast spin relaxation. As clearly shown in Fig. 10-8, the initial spectrum measured at 60 ns after the laser excitation showed an emissive polarization, which was due to the usual p-type TM. This polarization was found to change as the delay time was increased. The spectrum measured at 200 ns after the excitation showed a strong absorptive polarization, which was proposed to be due to the d-type TM. Similar polarization changes were also observed for such dyes as erthrosin B (FlLi ) and dibromofluorescein (FlBr2 ) which contain heavy atoms. On the other hand, an emissive polarization was only observed for the reaction of fluoresein (Fl ), which contain no heavy atom. From these results, Tero-Kubota et al. concluded that the strong absorptive... 

Figure 17. (a) Duroquinone radical anion, (b) Asymmetric duroquinone radical anion-imidazole complex. 

A direct evidence for the existence of triple-ions has been provided by the ESR studies of THF solutions of sodium salts of duroquinone radical anions in the presence of... 

Figure 5 FT EPR spectrum of duroquinone radical-anion, durosemiquinone radical as well as triethylamine radical cation and hydroxymethyl radical at a delay time of 100 ns. The simulation of the experimental spectrum is shown in Boltzmann equilibrium. Sample 1 mM DQ with 1 mM TEA in methanol (Reprinted with permission from Ref. 76)...

Photochemistry of quinones (1,4-benzoquinone, duroquinone, 2,6-di-t-butylbenzo-quinone, etc.) radical anions was studied in detail [173a]. According to cyclic voltammetry data in various solvents, the quinones showed typical reversible two-wave voltammograms, corresponding to two successive one-electron transfers [(5.22), (5.23)] to the radical anion then to the dianion ... 

The polarographic reduction of i/4-diene complexes was first noted for [M(i/4-l,4-quinone)Cp] (M = Rh or Ir, quinone = duroquinone or 2,6-di(t-butyl)quinone), which show one two-electron wave (M = Ir), or two one-electron waves (M = Rh) at potentials more negative than those of the free quinone (575). The cyclopentadienone compounds [M(i/4-C5R40)Cp] (M = CoorRh, R = Ph or C6F5) undergo reversible one-electron reduction to radical anions (e.g., M = Co, R = Ph, E° = — 1.46 V in thf). The cobalt complexes, more stable than those of rhodium, are generated by alkali metal reduction at 100 K and show ESR spectra characteristic of metal-based d9 species (374). 

Radiolytic reduction reactions have been carried out on substrates such as quinones, benzophenone, methyl viologen, and nitroaromatic compounds. In [mtba] [TfjN], the principal reactions were reduction of the substrates by solvated electrons and organic radicals derived from the solvent For example, irradiation of benzoquinone (BQ) or duroquinone (DQ) resulted in the formation of the protonated semiquinone radical, with the proton formed by radiolysis of [mtba] [TfjN] (Equation 5.7). The addition of triethylamine to capture the protons resulted instead in the formation of the semiquinone radical anions (Equation 5.8). 

Fig. 6 Passage from the stepwise to the concerted mechanism upon decreasing the driving force. Left potential energy profiles. Right reaction of 4-nitrocumyl chloride with homogeneous donors diamonds 2-nitropropanate ion, squares duroquinone anion radical, circles RNu -. E electrode potential or standard potential of a homogeneous donor.

Fig. 10-8. CIDEP spectra of duroquinone anion radical generated by the photoinduced electron transfer from triplet eosin Y in 1-propanol at room temperature. The delay times of the CIDEP measurement after the laser excitation (Nd YAG at 532 nm) are shown. (Reproduced from Ref. [9] by permission from The American Chemical Society)...

For a certain N the R values are calculated by adding the numbers immediately to the left and the right in the row for N-1. Thus, not only the strength of the coupling but also the number of nuclei is obtained from the analysis. When the number of equivalent nuclei is very large it may be difficult to observe all lines as shown in the next example, the duroquinone anion radical. 

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