Olefin, also called alkene, is a compound made up of hydrogen and carbon that contains one or more pairs of carbon atoms linked by a double bond. Olefins are examples of unsaturated hydrocarbons (compounds that contain only hydrogen and carbon and at least one double or triple bond). They are classified in either or both of the following ways: (1) as cyclic or acyclic (aliphatic) olefins, in which the double bond is located between carbon atoms forming part of a cyclic (closed-ring) or of an open-chain grouping, respectively, and (2) as monoolefins, diolefins, triolefins, etc., in which the number of double bonds per molecule is, respectively, one, two, three, or some other number.
Acyclic monoolefins have the general formula CnH2n, C being a carbon atom, H a hydrogen atom, and n an integer. They are rare in nature but can be formed in large quantities through industrial processing. One of the first processes used to produce them, developed in the early 20th century, was thermal cracking (breaking down of large molecules) of petroleum oils to gasoline. Olefins later were also produced via fluid catalytic cracking, steam cracking, and hydrocracking.
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