8annulene

8annulene, also known as cyclooctatetraene or COT, is a cyclic hydrocarbon with the chemical formula C8H8. It is an organic compound belonging to the annulene class, which are monocyclic hydrocarbons with alternating single and double bonds. 8annulene is a colorless liquid at room temperature.

Structurally, 8annulene is a planar ring of eight carbon atoms, each bonded to one hydrogen atom. The arrangement of double bonds suggests aromaticity, but 8annulene does not follow Hückel's rule for aromaticity, which requires 4n+2 pi electrons. 8annulene has 8 pi electrons, placing it in the category of antiaromatic compounds. However, it avoids antiaromaticity by adopting a non-planar, tub-shaped conformation. This conformational flexibility allows it to delocalize its electrons and behave more like a conjugated polyene than a true antiaromatic system.

8annulene can be synthesized through various methods, including the cyclization of acetylenes. It is a reactive molecule and readily undergoes addition reactions, characteristic of alkenes. It also participates in Diels-Alder reactions. Due to its unique electronic structure and reactivity, 8annulene has been a subject of significant interest in organic chemistry research, particularly in the study of aromaticity and conjugated systems.