Occurs naturally in ripening fruit and is used artificially to accelerate fruit ripening, e.g in banana transportation Although ethylene is a relatively simple molecule, its spectrum is considered to be one of the most difficult to explain adequately from both a theoretical and practical perspective. For this reason, it is often used as a test case in computational chemistry. Of particular note is the difficulty in characterizing the ultraviolet absorption of the molecule. Interest in the subtleties and details of the ethylene spectrum can be dated back to at least the 1950s.; Ethylene is a key component in Levinstein sulfur mustard, a chemical weapon agent.; Ethylene is an extremely important building block in the petrochemical industry. It can undergo many types of reactions which leads to a plethora of major chemical products. A list of some major types of reactions includes, 1) polymerization, 2) oxidation, 3) halogenation and hydrohalogenation, 4) alkylation, 5) hydration, 6) oligomerization, 7) hydroformylation, and 8) a ripening agent for fruits and vegetables (see Physiological responses of plants).; Ethylene oxide is a key raw material in the production of surfactants and detergents. It is also used to manufacture ethylene glycol (widely used as an automotive antifreeze), higher molecular weight glycols, and glycol ethers.; Production of ethylene in mineral oil-filled transformers is a key indicator of severe localized overheating (>750 °C).; The double bond is a region of high electron density, and most reactions occur at this double bond position.; This hydrocarbon has four hydrogen atoms bound to a pair of carbon atoms that are connected by a double bond. All six atoms that comprise ethylene are coplanar. The H-C-H angle is 119°, close to the 120° for ideal sp² hybridized carbon. The molecule is also relatively rigid: rotation about the C-C bond is a high energy process that requires breaking the ?-bond, while retaining the ?-bond between the carbon atoms. Used as a food additive [EAFUS]