Ethylene oxide, also called oxirane, is the organic compound with the formula C2H4O. It is a cyclic ether. This means that it is composed of 2 alkyl groups attached to an oxygen atom in a cyclic shape (circular). This colorless flammable gas with a faintly sweet odor is the simplest epoxide, a three-membered ring consisting of two carbon and one oxygen atom. Because of its special molecular structure, ethylene oxide easily participates in the addition reaction, opening its cycle, and thus easily polymerizes. Ethylene oxide is isomeric with acetaldehyde.