Benzofuroxans: A Possible +100 Years Old Misunderstanding?

Since 1912 benzofuroxans have been believed to exhibit a molecular structure characterised by the presence of two fused rings, i. e. a benzene ring and a pentatomic heterocycle containing a N-O-N fragment wherein one of the two N atoms is involved in a further N <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:semantics><mml:mo>→</mml:mo> <mml:annotation>${\to }$</mml:annotation> </mml:semantics> </mml:math> O bond, namely benzo[1,2-c]1,2,5-oxadiazole N-oxide. In this work, quantum chemical calculation results along with vibrational spectroscopic data raise fundamental questions about the electronic structure and the molecular topology of some 4,6-dinitro-derivatives of this class of compounds. An alternative interpretation is offered corroborated by the experimental vibrational and electronic spectra.