What is "cyclooctadecanonaene"

n. (context organic compound English) An annulene having 18 carbon atoms and 9 double bonds

Cyclooctadecanonaene or [18]annulene is an annulene with chemical formula . This hydrocarbon obeys Hückel's rule and is, therefore, an aromatic compound. Theoretical studies show that [18]annulene has only three completely delocalized π bonds associated with its aromaticity, while other six π bonds represent the conjugated 3c-2e π bonds on the periphery of [18]annulene. The compound was first synthesised by Franz Sondheimer.