isoprene
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Isoprene, also known as 2-methyl-1,3-butadiene (CH2=C(CH3)CH=CH2), is a derivative of 1,3-butadiene. Isoprene is a conjugated diene (see Diels-Alder reaction). It is a colorless liquid made by destructive distillation of rubber or from petroleum, and used to make synthetic rubber. It is the basic unit of plant products, including carotenoids, sterols, and terpenes.