Radical Cations and Radical Anions of Three Bridgehead Azopolycycloalkanes: A fluid-solution ESR study

The radical mono-ions of three azoalkanes in which the azo group is connected to the polycyclic alkane moieties at the bridgehead C-atoms, i.e. 1,1′-azonorbornane ( 1 ), 1,1′-azotwistane ( 2 ), and 1,1′-azobicyclo[3.2.1]octane ( 3 ), were studied in fluid solution by ESR spectroscopy. According to the ESR parameters and MO models, the radical cations of 1–3 should be considered as σ radicals, whereas the corresponding radical anions are π radicals. INDO calculations point to a a remarkable dependence of the ¹⁴N-coupling constants on the geometry at the N-atoms in the radical cations of aliphatic azo compounds.