The molecular configuration of bis(trifluoromethyl)nitroxide (CF3)2NO

Anisotropic 14N couplings have been determined using electron paramagnetic resonance spectroscopy for the radicals, bis(trifluoromethyl)nitroxide and di-tert-butylnitroxide as isolated in a polycrystalline fluorotrichloromethane matrix at 77 K. The results show that the nitrogen 2pz orbital spin-population in bis(trifluoromethyl)nitroxide is 26%, as compared with 48% in di-tert-butylnitroxide, which is due mainly to the importance of the oxygen-localised canonical structure (CF3)2N–O and to spin-delocalisation onto the CF3 groups: it is the large oxygen atom spin density of 0.63 that determines the relatively high reactivity of bis(trifluoromethyl)nitroxide in hydrogen-atom transfer reactions. On the basis of their anisotropic and isotropic 14N couplings (measured in liquid fluorotrichloromethane), it is concluded that the configuration at the nitrogen centre is near-planar in both nitroxides. This result is supported by molecular orbital calculations made on these, and related molecules in order to evaluate some of the theoretical methods available to organic chemists.