ESR Relaxation Studies on Orbitally Degenerate Free Radicals. II

Careful linewidth and saturation studies were performed on several orbitally degenerate hydrocarbon free radicals in liquid solution as a function of temperature, solvent, and counterion, and these are compared with similar studies on nondegenerate hydrocarbon free radicals. The anomalous $T_1\text{'}\mathrm{s}$ and $T_2\text{'}\mathrm{s}$ attributed to the orbital degeneracy are found to be strikingly independent of all these variables. This is most clearly evidenced for the coronene and triphenylene anion radicals. The results for the benzene and cyclo‐octatetraene anions (alkali metal prepared) are complicated by a further contribution to $T_2^{\text{−1}}$ which increases with temperature. This contribution is correlated with counterion and solvent dependent ion‐pairing effects. The intrinsic temperature‐independent $T_2^{\text{−1}}\text{'}\mathrm{s}$ for the orbitally degenerate free radicals are surprisingly well correlated with the small but anomalous deviations of the $g$ values for these radicals from the Segal, Kaplan, and Fraenkel experimental fit to Stone's theory of $g$ values. This is taken as positive evidence for the role of anomalous spin–orbit interactions in the mechanism(s) yielding the anomalous relaxation times. Their independence of temperature, solvent, and counterion suggests that the relaxation mechanism(s) is largely intramolecular.