27808-54-4Relevant articles and documents
Furoxan rearrangement of some pyridofuroxan derivatives studied by 1H, 13C, 14N, 15N and 17O NMR spectroscopy
Cmoch,Kamienski,Kamienska-Trela,Stefaniak,Webb
, p. 480 - 488 (2007/10/03)
Pyridofuroxan ([1,2,5]oxodiazolo[3,4-b]pyridine 1-oxide) undergoes isomerization between the N1-oxide and N3-oxide forms which can be observed by the 1H, 13C and 15N NMR spectroscopy but not by 14N and 17O NMR at ambient and low temperatures. The rearrangement becomes slower at low temperatures and at 233 K 1H NMR signals for the two structures become observable. 1H, 13C and 15N chemical shifts and 1H-1H, 13C-1H and 13C-13C coupling constants are used to characterize both forms in the equilibrium mixture. From the 1H NMR integrals at 233 K equilibrium constants are calculated. Protonation studies using trifluoroacetic acid as a solvent showed the favoured site of protonation to be the pyridine N4 nitrogen atom. DFT shielding calculations are reported for the 13C, 15N and 17O nuclei which support the assignments given. From the point of view of structural changes, 1JCC data for 8-nitrotetrazolo[1,5-a]pyridine and o-nitroaminopyridine as precursors of the pyridofuroxans are given for comparison purposes. X-ray diffraction data on 5-methoxypyridofuroxan support the structural results obtained from the NMR investigations. Copyright