isocyanide, any of a class of organic compounds having the molecular structure R―N+ ≡ C, in which R is a combining group derived by removal of a hydrogen atom from an organic compound. The isocyanides are isomers of the nitriles; they were discovered in 1867 but have never achieved any large-scale utility. They are usually prepared from primary amines by treatment with chloroform and alkali and often are obtained as minor products in the synthesis of nitriles from metal cyanides and organic halogen compounds. They possess remarkably powerful and repulsive odours.