n. (context organic compound English) A cycloalkene having an eight-membered ring and alternating single bond and double bonds; being nonplanar, it is not aromatic
1,3,5,7-Cyclooctatetraene (COT) is an unsaturated derivative of cyclooctane, with the formula CH. It is also known as  annulene. This polyunsaturated hydrocarbon is a colorless to light yellow flammable liquid at room temperature. Because of its stoichiometric relationship to benzene, COT has been the subject of much research and some controversy.
Unlike benzene, CH, cyclooctatetraene, CH, is not aromatic, although its dianion, ( cyclooctatetraenide), is. Its reactivity is characteristic of an ordinary polyene, i.e. it undergoes addition reactions. Benzene, by contrast, characteristically undergoes substitution reactions, not additions.