Electron spin resonance study of carbon-13 enriched 1,4-dinitrobenzene anion radical

Synthesis of 1,4-dinitrobenzene enriched to 30 at. per cent in carbon-13 at position 1 has been achieved. It has, therefore, been possible to examine the carbon-13 isotropic hyperfine interaction, ac, in the corresponding anion radical in a variety of solvent media. In dry dimethylformamide ac=2·36 gauss. The value of ac diminished nearly linearly with the mole fraction of water added to the DMF and reached a value of 1·45 gauss when the mole fraction of water was 0·428. In combination with previous results for 1,4- dinitrobenzene anion radical enriched in oxygen-17, the present observations provide experimental data concerning the unpaired spin densities at all the atomic positions in this radical. Together, these results are used to examine the spin density distribution in the radical; comparison is made with theoretical spin density distributions calculated by several molecular orbital methods.