Hyperfine data and g factors are reported for the radical cations of tetrathiafulvalene (TTF; 1) and of its derivatives 2–13. From the intense satellite spectra of 1+–13+ not only the coupling constants of the 33S isotopes in the TTF moiety could be determined, but also, in favourable cases, those of the 13C isotopes in the central double bond. The former values range from 0.370 (8+) to 0.470 mT (4+) and the latter from 0.255 (8+) to 0.360 mT (4+) in the radical cations of bis(ethylenedithio)‐TTF (8+) and tetracyano‐TTF (4+). The radical cation of TTF (1+) exhibits intermediate values, 0.425 for the 33S and 0.285 mT for the 13C isotopes. The spin population in 1+–13+ resides, to a large extent, in the central S2C  CS2 part of the π‐system. It tends to increase (decrease) by substitution with electron‐accepting (donating) groups in the 2,3,6,7‐positions of TTF.

Hyperfine data and g factors are reported for the radical cations of tetrdthiafuivalene (TTF; 1) and of its derivatives 2-13. From the intense satellite spectra of lt-13f not only the coupling constants of the 33S isotopes in the TTF moiety could be determined, but also, in favourable cases, those of the I3C isotopes in the central double