In organic chemistry a diene [pronounced /ˈdaɪ.iːn/ DYE-een] or diolefin [pronounced /daɪˈoʊləfɨn/ dye-OH-lə-fin] is a hydrocarbon that contains two carbon double bonds. Conjugated dienes are functional groups, with a general formula of C4R6. Dienes occur occasionally in nature but are widely used in the polymer industry.
Dienes can be divided into three classes, depending on the relative location of the double bonds:
Compounds that contain more than two double bonds are called polyenes. Polyenes and dienes, share many of their properties.
Synthesis of dienes
On an industrial scale, butadiene is prepared by thermal cracking of butanes. In a similarly non-selective process, dicyclopentadiene is obtained from coal tars.
In the laboratory, more directed and more delicate processes are employed such as dehydrohalogenations and condensations. Myriad methods have been developed, such as the Whiting reaction. Families of nonconjugated dienes are derived from the oligomerization and dimerization of conjugated dienes. For example, 1,5-cyclooctadiene and vinylcyclohexene are produced by dimerization of 1,3-butadiene.
Diene-containing fatty acids are biosynthesized from acetyl CoA.
Reactivity and uses
The most heavily practiced reaction of alkenes, dienes included, is polymerization. Butadiene is a precursor to rubber used in tires, and isoprene is the precursor to natural rubber. Chloroprene is a related but synthetic monomer.
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