Stereoelectronic effect at nitrogen in 2,6-di-tert-butyl-4-(N,N-disubstituted aminomethyl)phenoxyl radicals

Abstract

A variety of 2,6-di-tert-butyl-4-(N,N-disubstituted aminomethyl)phenoxyl radicals have been studied with respect to the para substituents’ and meta protons’ coupling constants observed in EPR and ENDOR experiments. For all molecules considered, restricted rotation dominates the spectroscopic features of the β-nuclei, and this plays a key role throughout the investigation. Based on the well-known McConnell–Heller equation, an empirical formula is proposed for analyzing the conformation at the α-carbon atom relative to the aroxyl plane. The results obtained reveal a strong stereoelectronic interaction between the β-nitrogen atom and the aromatic π-system. Hence, sterically unfavorable orientations are found to be preferred. The stereoelectronic interdependence is finally interpreted in terms of the generalized anomeric effect.

References

1. E. Müller and K. Ley, Z. Naturforsch., Teil B, 1953, 8, 694.
2. C. D. Cook and R. C. Woodworth, J. Org. Chem., 1953, 18, 261.
3. R. C. Sealy, L. Harman, P. R. West and R. P. Mason, J. Am. Chem. Soc., 1985, 107, 3401.
4. G. Lassmann, J. Curtis, B. Liermann, R. P. Mason and T. E. Eling, Arch. Biochem. Biophys., 1993, 300, 132.
5. C. Tommos, X. S. Tang, K. Warncke, C. W. Hoganson, S. Styring, J. McCracken, B. A. Diner and G. T. Babcock, J. Am. Chem. Soc., 1995, 117, 10 325.
6. J. K. Becconsall, S. Clough and C. Scott, Trans. Faraday Soc., 1960, 56, 459.
7. T. J. Stone and W. A. Waters, J. Chem. Soc., 1964, 213.
8. A. G. Davies, J. A. Howard, M. Lehnig, B. P. Roberts, H. B. Stegmann and W. Uber, in Landolt-Börnstein, Zahlenwerte und Funktionen aus Naturwissenschaften und Technik, vol. 9/c2, Springer-Verlag, Berlin, Heidelberg, New York, 1979; G. Deuschle, D. Klotz and H. B. Stegmann, ibid., vol. 17/e, 1988.
9. A. D. McLachlan, Mol. Phys., 1958, 1, 233.
10. A. D. McLachlan, Mol. Phys., 1960, 3, 237.
11. Y. Qin and R. A. Wheeler, J. Am. Chem. Soc., 1995, 17, 6083.
12. K. Scheffler and H. B. Stegmann, Elektronenspinresonanz, Springer-Verlag, Berlin, 1970.
13. J. E. Wertz and J. R. Bolton, Electron Spin Resonance – Elementary Theory and Practical Applications, McGraw-Hill, New York, 1972.
14. N. M. Atherton, Principles of Electron Spin Resonance, Ellis Horwood, Chichester, 1993.
15. E. W. Stone and A. H. Maki, J. Chem. Phys., 1962, 37, 1326.
16. K. Scheffler, K. Hieke, P. Schuler and H. B. Stegmann, Z. Naturforsch., Teil A, 1976, 31, 1620.
17. V. Fischer, W. Bühler and K. Scheffler, Z. Naturforsch., Teil A, 1983, 38, 570.
18. E. Jörβ, Dissertation, Universität Tübingen, 1996.
19. H. M. McConnell and D. B. Chesnut, J. Chem. Phys., 1958, 28, 107.
20. C. Heller and H. M. McConnell, J. Chem. Phys., 1960, 32, 1535.
21. K. Mukai, H. Nishiguchi, K. Ishizu, Y. Deguchi and H. Takaki, Bull. Chem. Soc. Jpn., 1967, 40, 2731.
22. Y. Oishi, K. Mukai, N. Nishiguchi, Y. Deguchi and H. Takaki, Tetrahedron Lett., 1968, 46, 4773.
23. W. T. Dixon, M. Moghimi and D. Murphy, J. Chem. Soc., Faraday Trans. 2, 1974, 1713.
24. H. B. Stegmann, K. Ulmschneider, P. Schuler, T. Jülich and K. Scheffler, Z. Naturforsch., Teil B, 1984, 39, 1416.
25. A. Carrington and P. F. Todd, Mol. Phys., 1965, 8, 299.
26. M. Jäger and H. B. Stegmann, Angew. Chem., 1996, 108, 1943; Angew. Chem., Int. Ed. Engl., 1996, 35, 1815.
27. V. Fischer, Dissertation, Universität Tübingen, 1981.
28. A. J. Kirby, The Anomeric Effect and Related Stereoelectronic Effects at Oxygen, Springer-Verlag, Berlin, Heidelberg, New York, 1983.
29. M. Mäurer, W. Hiller, B. Müller and H. B. Stegmann, Chem. Ber., 1992, 125, 857.
30. J. C. Matasyoh, P. Schuler, H. B. Stegmann, J. L. Poyer, M. West and E. G. Janzen, Magn. Res. Chem., 1996, 34, 351.
31. J. Herdan, A. T. Balaban, N. Negoita and N. Grecu, Rev. Roum. Chim., 1983, 28, 129.
32. F. R. Hewgill and R. J. Webb, Aust. J. Chem., 1977, 30, 2565.