isoprene

I"so*prene, n. Etym: [Etymol. uncertain.] (Chem.) Defn: An oily, volatile hydrocarbon, obtained by the distillation of caoutchouc or guttaipercha.C5H8 -- unsaturated, and used to make synthetic rubber by polymerization. In organic chemistry, viewed conceptually as the building block of the terpene series of hydrocarbons

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