Physicochemical Properties of Azafulvalenes

Although azafulvalenes as yet comprise a small class of cyclic cross-conjugated compounds, they have been the subject of a variety of theoretical investigations spanning a range from the Hiickel (HMO) theory to the 

Semiempirical calculations (MNDO//MNDO) have been performed for sesquifulvalene 6 and its aza analogs 11 (R = Me), 12 (R = Me), 72a/72b, and 73a/73b (91JOC4223). In all cases the most stable conformation is the planar one (S AH 0). The calculated barrier of rotation around the cen- 

Among the variety of nitrogen-containing fulvalenes emerging from types 7-14, X-ray structural determinations have been performed on about 20 representative examples. The first crystal structure determination was carried out by application of the folding-molecule method on 3,3 -diphenyl-l,T-bi-isoindolylidene 64 (R = H) (71CB3108).The dimeric isoindolenine system 

In the course of the investigations directed at the structural characterization of another type of aza analog of sesquifulvalene, the X-ray structure of the triaza derivative 72a was determined (89CC1086). The molecule is effectively planar, the torsion angle between the pyridine and benzimidazole 

Recently, the structure of the bis-imidazo fused 1,4,5,8-tetraazafulvalene 141a (anti-isomer) was reported (97LAR617). The ideal planarity of the tetraazafulvalene framework is striking the exocyclic aryl residues are slightly bent out of the plane. As expected, the central C—C distance 

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