Linewidths and Spin Densities in the ESR Spectra of Electrogenerated Radical Anions of Sterically Hindered 2,2′‐Dinitrobiphenyl and 1,8‐Dinitronaphthalene

The ESR spectra of the radical anions of 2,2′‐dinitrobiphenyl and 1,8‐dinitronaphthalene generated by electroreduction in anhydrous dimethylformamide (DMF) have been recorded in the temperature range 20 to −80°C. Interesting linewidth effects are observed in the ESR spectra of these two radical anions at lower temperatures. From the linewidth data, the spectral densities for the modulations of isotropic splittings and anisotropic intramolecular interactions have been computed making use of the complete expressions for linewidths derived from relaxation matrix theory and a two‐jump model. Using the spectral densities and the measured dynamic frequency shifts, correlation times for modulations of isotropic splittings are evaluated. It is noticed that the two‐jump model with out‐of‐phase correlation of nitrogen splittings in the two nitro groups explains the observed trends in the spectral densities satisfactorily for both the radical anions. The details of the modulating motions are investigated next, and s...

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