Antiaromatic compounds

Cyclobutadiene is an organic compound with the formula . It is very reactive owing to its tendency to dimerize. Although the parent compound has not been isolated, some substituted derivatives are robust and a single molecule of cyclobutadiene is quite stable. Since the compound degrades by a bimolecular process, the species can be observed by matrix isolation techniques at temperatures below 35 K. It is thought to adopt a rectangular structure.

1,3,5,7-Cyclooctatetraene (COT) is an unsaturated derivative of cyclooctane. It is a colorless flammable liquid at room temperature. COT is an antiaromatic compound as it possesses 8 π electrons. In contrast to the aromaticity commonly seen in benzene rings; antiaromaticity destabilises the COT molecule. This destabilisation effect is so strong that COT avoids it by adopting a non-planar 'tub' conformation, which prevents all of the π orbitals from forming a single conjugated system. As a result, COT possesses significant polyene character and will undergo many reactions that benzene rings wil

Oxirene is a heterocyclic chemical compound which contains an unsaturated three-membered ring containing two carbon atoms and one oxygen atom. The molecule was synthesized in low temperature ices and detected upon sublimation by isomer selective photoionization reflectron time-of-flight mass spectrometry.

In organic chemistry, thiepine (or thiepin) is an unsaturated seven-membered heterocyclic compound, with six carbon atoms and one sulfur atom. The parent compound, C6H6S is unstable and is predicted to be antiaromatic. Bulky derivatives have been isolated and shown by X-ray crystallography to have nonplanar C6S ring.

Antiaromaticity is a chemical property of a cyclic molecule with a π electron system that has higher energy, i.e., it is less stable due to the presence of 4n delocalised (π or lone pair) electrons in it, as opposed to aromaticity. Unlike aromatic compounds, which follow Hückel's rule ([4n+2] π electrons) and are highly stable, antiaromatic compounds are highly unstable and highly reactive. To avoid the instability of antiaromaticity, molecules may change shape, becoming non-planar and therefore breaking some of the π interactions. In contrast to the diamagnetic ring current present in aromati

1,2-Dioxin is a heterocyclic, organic, antiaromatic compound with the chemical formula CHO. It is an isomeric form of 1,4-dioxin (or p-dioxin).

Biphenylene is an organic compound with the formula (C6H4)2. It is a pale, yellowish solid with a hay-like odor. Despite its unusual structure, it behaves like a traditional polycyclic aromatic hydrocarbon.

Pentalene is a polycyclic hydrocarbon composed of two fused cyclopentadiene rings. It has chemical formula . It is antiaromatic, because it has 4n π electrons where n is any integer. For this reason it dimerizes even at temperatures as low as −100 °C. The derivative 1,3,5-tri-tert-butylpentalene was synthesized in 1973. Because of the tert-butyl substituents this compound is thermally stable. Pentalenes can also be stabilized by benzannulation for example in the compounds benzopentalene and dibenzopentalene.

Acepentalene is a tricyclic anti-aromatic compound. Its molecular formula is . It consists of three five-membered rings fused across three of the five carbon atoms. The central carbon atom in acepentalene is part of all three rings. There are formally five double bonds in acepentalene, so that the molecule formally contains four double bonds on the exterior, and one double bond from the central carbon to the exterior of the ring system.