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either of two aliphatic organic compounds that have the formula C4H6. The term ordinarily signifies the more important of the two, 1,3-butadiene, which is the major constituent of many synthetic rubbers. It was first manufactured in Germany during World War I from acetylene. During World War II, butenes from petroleum and natural gas were the raw material for 60 percent of American butadiene production, ethyl alcohol for the rest. Butadiene rubber has now completely displaced natural rubber in the manufacture of automobile tires. Nearly all butadiene is made by dehydrogenation of butane or butenes or by high-temperature cracking (breaking up of large molecules) of petroleum distillates.