Isoprene \I"so*prene\, n. [Etymol. uncertain.] (Chem.) An oily, volatile unsaturated hydrocarbon ({C5H8}), obtained by the distillation of caoutchouc or gutta-percha, and used to make synthetic rubber by polymerization. In organic chemistry, it is viewed conceptually as the building block of the terpene series of hydrocarbons. [1913 Webster +PJC]
Pentine \Pen"tine\, n. [See {Penta-}.] (Chem.) An unsaturated hydrocarbon, {C5H8}, of the acetylene series. Same as {Valerylene}. [1913 Webster]
Valerylene \Val`er*yl*ene\, n. (Chem.) A liquid hydrocarbon, {C5H8}; -- called also {pentine}. [1913 Webster]