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Radical cations and anions of pyrazines: an electron paramagnetic resonance study

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Eiermann,  Uwe
Department of Organic Chemistry, Max Planck Institute for Medical Research, Max Planck Society;

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Neugebauer,  Franz A.
Department of Organic Chemistry, Max Planck Institute for Medical Research, Max Planck Society;

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Citation

Eiermann, U., Neugebauer, F. A., Chandra, H., Symons, M. C. R., & Wyatt, J. L. (1992). Radical cations and anions of pyrazines: an electron paramagnetic resonance study. Journal of Chemical Society, Perkin Transactions 2, 1: 1/04582B, pp. 85-89. doi:10.1039/P29920000085.


Cite as: https://hdl.handle.net/11858/00-001M-0000-0019-AC22-2
Abstract
Dilute solutions of a series of pyrazines (1–13) in CFCl3 at 77 K were exposed to 60Co γ-rays, generating the corresponding radical cations which were identified by their EPR spectra. Two distinct types of spectra were observed. Those obtained from mono- and di-methyl derivatives showed large hyperfine coupling to two 14N nuclei similar to that of the parent pyrazine cation and are assigned to n(σ)-radical cations. The other spectra observed for the tetramethyl, OCH3, SCH3 and NR2 derivatives are assigned to π-radical cations. These findings confirm that the SOMO has switched from n(σ) to π between the dimethyl derivatives 4, 6 and 8 and the tetramethyl compound 9, respectively. The NR2-substituted radical cations 12˙+ and 13˙+ were also observed in fluid solution. The corresponding radical anions 1˙––13˙–, studied in solid solution, show major hyperfine coupling to the two ring 14N nuclei. Studies in fluid solution indicate that strong electron donor substituents (OCH3, SCH3, NR2) convert the S-type π-SOMO of the pyrazine radical anion to a π-SOMO with predominant A-type character.