Azonine

Azonine is an unsaturated heterocycle of nine atoms, with a nitrogen atom replacing carbon at one position. A variety of derivatives have been synthesized. It possesses a considerable amount of aromatic stability. It and the anion of cyclononatetraene, C₉H₉^–, are the largest monocyclic all-cis ring systems to be aromatic and close to planar. Due to a balance between angle strain (~20°) and aromaticity, a planar conformation and distorted conformation are very close in energy and the two are observable as an equilibrium mixture in the solution phase in acetone. Furthermore, the presence of substituents or nearby cations strongly influences the conformation.