HINDERED INTERNAL ROTATION OF THE CF<sub>3</sub> GROUP IN THE 2-TRIFLUOROMETHYLNITROBENZENE RADICAL ANION IN DMF:H<sub>2</sub>O MIXTURES
The temperature dependences of the EPR spectrum of the 2-trifluoromethylnitrobenzene radical anion in DMF:H2O mixtures, caused by the dynamic modulation of the fluorine isotropic hyperfine interaction by the hindered internal rotation of the CF3 group, have been measured and reconstructed numerically. The activation energy of rotation (EF) and the dynamic mode depended on the water content in the mixture. For mixtures with a molar fraction of water χ = 0, 0.186, 0.315, 0.409, 0.534, 0.650, 0.810, and 0.910, EF = 34.70 kJ/mol, 41.31 kJ/mol, 42.30 kJ/mol, 38.41 kJ/mol, 37.01 kJ/mol, 34.51 kJ/mol, 24.10 kJ/mol, and 21.78 kJ/mol, respectively. For χ = 0.186 in the temperature ranges accessible for measurements, the dynamic exchange is slow; for χ = 0.315, 0.409, 0.534, and 0.650, transitions from slow to intermediate and fast exchange take place; for χ = 0.810 and 0.910 in the temperature ranges under study T∈[252, 309]; [254, 297] (K), the exchange is fast. In the range 0.6 EF decreased drastically, and the activation energy of rotational diffusion (Er) of the radical anion became maximum, which corresponds to the range of the compositions of DMF:H2O with maximum deviations from the ideal state.