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ESR and 1 H NMR studies of a new class of nitroxyl, nitronylnitroxyl and iminonitroxyl radicals
Author(s) -
Khramtsov V. V.,
Weiner L. M.,
Gogolev A. Z.,
Grigor'ev I. A.,
Starichenko V. F.,
Volodarsky L. B.
Publication year - 1986
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260240304
Subject(s) - chemistry , radical , electron paramagnetic resonance , substituent , protonation , delocalized electron , nitroxyl , deprotonation , photochemistry , medicinal chemistry , crystallography , nuclear magnetic resonance , organic chemistry , ion , physics
A new synthesis of nitronylnitroxyl (NNR), iminonitroxyl (INR) and nitroxyl radicals (NR) is suggested, involving oxidation of 4 H ‐imidazol di‐ N ‐oxides with O 2 or PbO 2 in the presence of nucleophilic reagents. This method allowed the preparation of radicals which could not be synthesized by known procedures. These radicals were studied by ESR and 1 H NMR spectroscopy. The hyperfine interaction constants of the NNR were measured and assigned (in some cases radicals containing 15 N were used). The influence of protonation and deprotonation of functional groups (OH, NH 2 ) in the NNR on their ESR spectra was investigated and the p K values of these radicals were measured by ESR. Differences between the ESR spectra of two isomeric INR were found, and the structures of these radicals were established by 1 H NMR. Changes in spin density delocalization in 3‐imidazoline 3‐oxide nitroxyl radicals were studied, and the spin density was found to be ‘pushed out’ to the peripheral fragments of these radicals on increasing the number of methoxy groups in the α‐position to the N—O . fragment. Hindered rotation around the σ‐bond of a bulky substituent in the α‐position to the N—O . fragment was detected by ESR. The activation energy of this hindered rotation was Δ E = 30±1.7 kJ mol −1 .