Abstract The crystal structure of the title compound, C8H20NO+.-CI-,(I), and the structures of its derivatives,(2-chloro-ethyl) diisopropylammonium chloride, C8HI9C1N+. CI-,(II), and diisopropyl (2-mercaptoethyl) ammonium chlo-fide, C8H20NS+. C1-,(III), are described. The conforma-tions of the isopropyl groups in (II)(gauche-gauche) are different from those in (I) and (III)(both gauche-trans). The structures are stabilized by hydrogen bonds of the type Y ...