CYCLOHEPTA-3,5-DIEN-1-YL 3,5-DINITROBENZOATE

The cyclohepta-3,5-diene ring in the title compound, C14H12N2O6, 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 sp(2)-C atoms. All but one of these examples adopts the C-2-symmetric (twist) conformation, despite the fact that experimental gas-phase and computational results show a C-2-symmetric (envelope) conformation for the free ring. The 'free' cyclohepta-3,5-diene in the title compound clearly adopts a C-s-symmetric conformation with C1 displaced from the plane of the other six ring atoms. The ring is forced to adopt the C-2-symmetric conformation in more complex systems so as to minimize unfavourable intramolecular non-bonded repulsions.