The quinones of bicyclo[3.1.0]hexatriene: A computational study of their chemistry and thermochemistry

Quinones of bicyclo[3.1.0]hexa-1,3,5-triene were examined computationally. The six compounds considered were the five possible classical and one non-classical quinone: bicyclo[3.1.0]hexa-1(6),4-diene-2,3-dione (and its monocyclic isomer with a long trans-annular bond), bicyclo[3.1.0]hexa-1(5),3-diene-2,6-dione, bicyclo[3.1.0]hexa-1,4-diene-3,6-dione (and its monocyclic isomer with a long trans-annular bond), and bicyclo[3.1.0]hexa-1(5),4-diene-2,4-dione-3,6-diyl, a non-classical (non-Kekulé) zwitterion. The two long trans-annular bond structures are akin to that found for m-benzyne. Geometries were calculated (BLYP/6-31G∗, CASSCF(2,2)/6-31G∗, MP2/6-31G∗) and electronic structural inferences were made from the geometries. Also calculated were relative energies and heats of formation (CBS-QB3), singlet and triplet energies (BLYP/6-31G∗), and ionization energies and electron affinities (HF/6-311+G∗∗//BLYP/6-31G∗). The NICS(1) calculations were performed as a probe of the aromaticity of the diverse quinones.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Five new bicyclo[3.1.0]hexa-1,3,5-triene quinones are explored quantum chemically. ► A nonclassical zwitterionic quinone of reasonable stability is uncovered. ► Shortbond-long bond isomerism is exhibited.