Oxepin is an oxygen-containing heterocycle consisting of a seven-membered ring with three double bonds. It exists as an equilibrium

Chemical equilibrium

In a chemical reaction, chemical equilibrium is the state in which the concentrations of the reactants and products have not yet changed with time. It occurs only in reversible reactions, and not in irreversible reactions. Usually, this state results when the forward reaction proceeds at the same...

 mixture with benzene oxide. The oxepin-benzene oxide system has fluctuating bonds in which the equilibrium can be shifted to one extreme or the other by suitable substituents. This compound is not aromatic.