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.