Temperature dependence of EPR spectrum of 2-trifluoromethylnitrobenzene radical anion in acetonitrile

Temperature dependence of the EPR spectrum of 2-trifluoromethylnitrobenzene radical anion in anhydrous acetonitrile in the temperature range 217 K ≤ T ≤ 296 K was studied and simulated. Temperature-dependent dynamic modulation of the fluorine isotropic hyperfine structure is caused by slow hindered rotation of CF3 group with an activation energy of E F* = 36.5±0.5 kJ mol−1, which is the highest value for motions in π-type free radicals studied to date.