Electron self-exchange kinetics between 2,3-dicyano-5,6-dichloro-p-benzoquinone (DDQ) and its radical anion. Part 1. Solvent dynamical effects †

Abstract

Rate constants of the electron self-exchange between 2,3-dicyano-5,6-dichloro-p-benzoquinone (DDQ) and its radical anion (DDQ^˙–) are measured by means of EPR-line-broadening effects in different solvents at T = 293 K. Solvents of different polarity like CHCl₃, CH₂Cl₂, CH₃CN, benzonitrile and acetone were used. No correlation is found in the sense of the classical Marcus theory, where ln k_et should depend linearly on the solvent parameter γ = 1/n² – 1/ε_s (n = refractive index, ε_s = static relative permittivity of the solvent). The investigated γ-range was 0.270 ≤ γ ≤ 0.530. The diffusion corrected rate constants k_et cover a range of 8.9 to 36.7 × 10⁸ M^–1 s^–1 and clearly show a solvent-dynamical effect, expressed by the longitudinal relaxation time τ_L dependence of the solvents used. The observed dynamical friction solvent effects clearly indicate an adiabatic reaction behaviour of this electron self-exchange reaction.

References

1. G. Grampp, in Electron Paramagnetic Resonance, Eds. B. C. Gilbert, N. M. Atherton and M. J. Davies, The Royal Society of Chemistry, Cambridge, 1999, vol. 16, pp. 234–267.
2. G. Grampp and W. Jaenicke, Ber. Bunsenges. Phys. Chem., 1984, 88, 325.
3. G. Grampp and W. Jaenicke, J. Chem. Soc., Faraday Trans. 2, 1985, 81, 1035.
4. G. Grampp and W. Jaenicke, Ber. Bunsenges. Phys. Chem., 1991, 95, 904.
5. T. T.-T. Li and C. H. Brubaker Jr., J. Organomet. Chem., 1981, 216, 223.
6. T. T.-T. Li, M. J. Weaver and C. H. Brubaker Jr., J. Am. Chem. Soc., 1982, 104, 2381.
7. D. Jürgen, S. U. Pedersen, J. A. Pedersen and H. Lund, Acta Chem. Scand., 1997, 51, 767.
8. R. Fuhlendorff, T. Lund, H. Lund and J. A. Pedersen, Tetrahedron Lett., 1987, 28, 5335.
9. H. Larsen, S. U. Pedersen, J. A. Pedersen and H. Lund, J. Electroanal. Chem., 1992, 331, 971.
10. M. J. Weaver and G. E. McManis III, Acc. Chem. Res., 1990, 23, 294.
11. M. J. Weaver, Chem. Rev., 1992, 92, 436.
12. H. Larsen, Y. A. Khan and G. Grampp, J. Chem. Soc., Perkin Trans. 2, 1997, 2555.
13. R. A. Marcus and N. Sutin, Biochem. Biophys. Acta, 1985, 811, 265.
14. R. A. Marcus, J. Chem. Phys., 1956, 24, 966.
15. R. A. Marcus, J. Chem. Phys., 1957, 26, 876.
16. N. Sutin, Prog. Inorg. Chem., 1983, 30, 441.
17. S. J. Formosinho, L. G. Arnant and R. Fausto, Prog. React. Kinet., 1998, 23, 1.
18. S. F. Nelsen, Y. Kim and S. C. Blackstock, J. Am. Chem. Soc., 1989, 111, 2045.
19. S. F. Nelsen, R. F. Ismagilov and D. A. Trieber II, Science, 1997, 278, 846.
20. G. Rauhut and T. Clark, J. Chem. Soc., Faraday Trans., 1994, 90, 1783.
21. G. Rauhut and T. Clark, J. Am. Chem. Soc., 1993, 115, 9127; R. M. Nelsen, J. T. Hupp and D. I. Yoon, J. Am. Chem. Soc., 1995, 117, 9085.
22. S. F. Nelsen, in Advances in Electron Transfer Chemistry, ed. P. S. Mariano, JAI Press Inc., London, 1991, vol. 3, pp. 167–189.
23. G. Grampp, Rev. Sci. Instrum., 1985, 56, 2050.
24. M. Oyama, F. Marken, R. D. Webster, I. A. Cooper, R. G. Compton and S. Okazki, J. Electroanal. Chem., 1998, 451, 193.
25. C. Corvaja, L. Pasimeni and M. Brustalon, Chem. Phys., 1976, 14, 177.
26. D. Gordon and M. J. Hove, J. Chem. Phys., 1973, 59, 3419.
27. B. Kirste, Anal. Chim. Acta, 1992, 265, 191.
28. G. Grampp and G. Stiegler, J. Magn. Reson., 1986, 70, 1.
29. G. Grampp, Spectrochim. Acta, Part A, 1998, 54, 2349.
30. R. W. Fawcett, Chem. Phys. Lett., 1992, 199, 153.
31. M. Bixon and I. Jortner, Chem. Phys., 1993, 176, 467.
32. H. Heitele, Angew. Chem., Int. Ed. Engl., 1993, 32, 359.
33. H. Sumi and R. A. Marcus, J. Chem. Phys., 1986, 84, 4894.
34. G. Grampp, W. Harrer and W. Jaenicke, J. Chem. Soc., Faraday Trans. 1, 1987, 83, 161.
35. W. Harrer, G. Grampp and W. Jaenicke, Chem. Phys. Lett., 1984, 112, 263.
36. G. Grampp, W. Harrer and G. Hetz, Ber. Bunsenges. Phys. Chem., 1990, 94, 1343.
37. A. Kapturkiewicz and B. Behr, J. Electroanal. Chem., 1984, 163, 189.
38. M. Opallo and A. Kapturkiewicz, Electrochim. Acta, 1985, 30, 1301.
39. W. R. Fawcett, Langmuir, 1989, 5, 661.
40. W. R. Fawcett and M. Opallo, J. Phys. Chem., 1992, 96, 2920.
41. G. Grampp, A. Kapturkiewicz and W. Jaenicke, Ber. Bunsenges. Phys. Chem., 1990, 94, 439.
42. S. F. Nelsen, personal communication.