SUBSTITUENT-DEPENDENT ELECTRON-TRANSFER IN RADICAL-ANIONS OF 9-DISUBSTITUTED AND 9,10-DISUBSTITUTED 2,7-DINITRO-9,10-DIHYDRO-9,10-ETHANOANTHRACENES

Radical anions from a series of 9-substituted- and 9,10-disubstituted- 2,6-dinitro- and 2,7-dinitro-9,10-dihydro-9,10-ethanoanthracenes were investigated by EPR spectroscopy at 25 degrees C. In the case of radic al anions of compounds with nitro groups in both the 2- and 6-position s, hyperfine coupling constants (HFCs) arose from hydrogen and nitroge n atoms on the aromatic ring bearing the nitro group together with a f urther coupling to one methylene proton of the bridging group anti to the nitro substituent. By contrast, radical anions derived from compou nds bearing nitro groups in both the 2- and 7-positions in a number of instances exhibited intramolecular electron transfer which was fast o n the EPR time-scale with respect to both nitrogen and hydrogen, with HFCs arising from magnetic nuclei on both nitrophenyl rings, with furt her coupling from two methylene protons of the bridging group. The rel ative rate on the EPR time-scale of electron transfer for the latter g roup of compounds showed a subtle substituent dependence. With tert-bu tyl or methyl groups in the 9-position, or nitro groups in both the 9- and 10-positions, localization of spin density to one nitrophenyl rin g resulted and HFCs were similar to those for the slow exchange system s.