Lead tetraacetate one-electron oxidation of nine different N-alkoxy-2,6dinitroanilines substituted with trifluoromethyl, methyl and nitro groups in position 4 yielded aminyl radicals for which hypertine 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-dinitrophenyla~ne with lead tetraacetate produced first the aminyl radical of the respective 2,Wnitro 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-methoxyand N-ethoxy-N-2,4,6-trinitrophenylaminyl radicals. Nitroxyl radicals were detected only under conditions where oxygen was present in the solvent.
An ipso-nitration was detected a t position 4 of N-methoxy-and N-ethoxy-N-(4-carboxy-2,6-dinitrophenyl)aminyl radicals upon oxidation of the corresponding amines with lead tetraacetate in toluene and in methylene chloride. A very fast substitution by the nitro group was also observed for another capto-dative aminyl radical, namely N-(3',S-di-tert-butylphenyl)-N-(4-carboxy-2,6-dinitrophenyl)aminyl. The hyperfine coupling constant of the aminyl nitrogen was established to be nearly the same for these aminyl radicals irrespective of the donor group bonded via the aminyl nitrogen to the polynitrophenyl group. The rotational correlation time of the aminyl radicals was determined. Kinetic measurements of N-ethoxy-N-(p-carboxy-2,6-dinitrophenyl)aminyl radical a t different temperatures (250-290 K) from EPR spectra provided further proof of the nitration reaction. Proton hyperfine couplings of a total of eight aminyl radicals, with their signs, were measured by ENDOR and TRIPLE resonance methods. The hyperfine coupling of aminyl nitrogen of N-(3',S-di-tert-butylphenyl)-N-(2,6-dinitrophenyl)aminyl radical was also measured by ENDOR; hyperfine couplings of the nitro group nitrogens at the 2,6-positions could not be measured but had non-zero hyperfine coupling according to EPR simulation. Protons at the 2',6'-positions of the tert-butyl-substituted phenyl ring were found to have unequal and invariant hyperfine coupling a t temperatures from 200 to 270 K, and the diarylaminyl radical was concluded by SYBYL calculation to have a twisted (unequal 2,6'-positions) structure.
Anipso‐nitration was detected at position 4 ofN‐methoxy‐ andN‐ethoxy‐N‐(4‐carboxy‐2,6‐dinitrophenyl)aminyl radicals upon oxidation of the corresponding amines with lead tetraacetate in toluene and in methylene chloride. A very fast substitution by the nitro group was also observed for another capto‐dative aminyl radical, namelyN‐(3′,5′‐di‐tert‐butylphenyl)‐N‐(4‐carboxy‐2,6‐dinitrophenyl)aminyl. The hyperfine coupling constant of the aminyl nitrogen was established to be nearly the same for these aminyl radicals irrespective of the donor group bonded via the aminyl nitrogen to the polynitrophenyl group. The rotational correlation time of the aminyl radicals was determined. Kinetic measurements ofN‐ethoxy‐N‐(p‐carboxy‐2,6‐dinitrophenyl)aminyl radical at different temperatures (250–290 K) from EPR spectra provided further proof of the nitration reaction. Proton hyperfine couplings of a total of eight aminyl radicals, with their signs, were measured by ENDOR and TRIPLE resonance methods. The hyperfine coupling of aminyl nitrogen ofN‐(3′,5′‐di‐tert‐butylphenyl)‐N‐(2,6‐dinitrophenyl)aminyl radical was also measured by ENDOR; hyperfine couplings of the nitro group nitrogens at the 2,6‐positions could not be measured but had non‐zero hyperfine coupling according to EPR simulation. Protons at the 2′,6′‐positions of thetert‐butyl‐substituted phenyl ring were found to have unequal and invariant hyperfine coupling at temperatures from 200 to 270 K, and the diarylaminyl radical was concluded by SYBYL calculation to have a twisted (unequal 2′,6′‐positions) structure.
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