Cyclohepta-3,5-dien-l-yi 3,5-Dinitro- benzoate

The cyclohepta-3,5-diene ring in the title compound, C14H12N206, is the first example of a 'free' ring to be characterized by crystal structure analysis. All previous examples are either bridged, fused to other rings or have exocyclic conjugative substituents attached to the ring sp2-C atoms. All but one of these examples adopts the C2-symmetric (twist) conformation, despite the fact that experimental gas-phase and computational results show a Cs-symmetfic (envelope) conformation for the free ring. The 'free' cyclohepta-3,5-diene in the title compound clearly adopts a Cs-symmetdc conformation with C1 displaced from the plane of the other six ring atoms. The ring is forced to adopt the C2