NMR SPECTRA OF CYCLIC NITRONES. 4. SYNTHESIS AND 13C NMR SPECTRA OF 4H-IMIDAZOLE N-OXIDES AND N,N-DIOXIDES

Article abstract of DOI:10.1007/BF00486679

4H-Imidazole 1,3-dioxides and 4H-imidazole 3-oxides were obtained by oxidation of 1-hydroxy-3-imidazoline 3-oxides and 1-hydroxy-3-imidazolines with lead and manganese dioxides or the stable nitroxyl radical, while 4H-imidazole 1-oxides were obtained by thermal decomposition of 1-acetoxy-3-imidazoline 3-oxides.Facile oxidation of the ethyl group in 5-ethyl-4H-imidazole 1,3-dioxide and the formation of 5-acetyl-4H-imidazole 3-oxide were observed.It is shown that a strictly determined region of chemical shifts of the C₍₂₎, C₍₅₎, and C₍₄₎ atoms is characteristic for each group of 4H-imidazole N-oxides in the 13C NMR spectra; this makes it possible to clearly establish the position of the N-oxide oxygen atom.