tabun (täˈbən) [key], liquid chemical compound used as a nerve gas. It boils at 240°C with some decomposition. The liquid is colorless to brownish; its vapors have a fruity odor similar to that of bitter almonds. The liquid is absorbed through the skin, but the vapor is not. Although tabun is destroyed by its reaction with bleaching powder, the poisonous gas cyanogen chloride is produced. Chemically, tabun is cyanodimethylaminoethoxyphosphine oxide.