Abstract 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 1 H, 13 C and 15 N NMR spectroscopy but not by 14 N and 17 O NMR at ambient and low temperatures. The rearrangement becomes slower at low temperatures and at 233 K 1 H NMR signals for the two structures become observable. 1 H, 13 C and 15 N chemical ...