Hyperfine couplings of N‐alkoxy‐N‐polynitrophenylaminyl radicals determined by ENDOR and TRIPLE resonance spectroscopy

Abstract

AbstractLead tetraacetate one‐electron oxidation of nine different N‐alkoxy‐2,6‐dinitroanilines substituted with trifluoromethyl, methyl and nitro groups in position 4 yielded aminyl radicals for which hyperfine couplings were measured by ENDOR and TRIPLE resonance spectroscopy. The optimum temperature range for proton ENDOR and general TRIPLE resonance measurements of aminyl radicals was 210–250 K and for nitrogen ENDOR 260 K in toluene. Further lowering for the temperature rapidly decreased the EPR intensity. The concentration of the sample and the amount of oxidant were optimized for obtaining ENDOR spectra. The relative signs of the hyperfine couplings of nitrogens, fluorines and protons were determined in the basis of general TRIPLE resonance experiments. The oxidation of N‐methoxy‐N‐2,6‐dinitrophenylamine and N‐ethoxy‐N‐2,6‐dinitrophenylamine with lead tetraacetate produced first the aminyl radical of the respective 2,6‐dinitro compound at low temperature (below 260 K) and very soon afterwards the aminyl radical of the respective 2,4,6‐trinitro compound, by a route in which hydrogen has to be removed from the system. Rotational correlation times were estimated for N‐methoxy‐and N‐ethoxy‐N‐2,4,6‐trinitrophenylaminyl radicals. Nitroxyl radicals were detected only under conditions where oxygen was present in the solvent.