ESR Studies of Nitrobenzene Ion-Pair Equilibria in N,N-Dimethylformamide

The hyperfine splitting constants of the nitrobenzene radical anion in DMF vary with the type of the counter cations and the concentrations. The tendency of these variations is related to the shift of the half-wave reduction potential of nitrobenzene. The variation of the nitrogen 14N hyperfine splitting constant is attributable to the formation of ion pairs involving the nitrobenzene radical anion and its counter cation. The ion-pair formation constants were evaluated from the changes in the hyperfine splitting and are completely consistent with those obtained from polarographic studies.