Monomer, dimers and trimers of cyanogen N-oxide, NC–CN→O. An X-ray, FVT-MS/IR and theoretical investigation

The structures of the trimers 4 and 5 of cyanogen N-oxide, NC–CNO 2 are established by X-ray crystallography and 13C NMR spectroscopy. Triethyl phosphite reduction of 4 and 5 affords the 1,2,4-oxadiazolyl-1,2,5-oxadiazole 6. Deoxygenation of the N-oxide moieties in furoxans 1, 4, and 5 also takes place easily on the walls of the mass spectrometer. FVT-MS and FVT-IR investigations of furoxans 1, 4, and 5 reveal that small amounts of cyano isocyanate, NC–NCO 3 accompany the formation of the main thermolysis product, NC–CNO 2. The isomerisation of 2 to 3 has a high calculated activation barrier but is catalysed efficiently by Ag2S. The IR and mass spectra of 3 are analysed.