olefin

—olefinic, adj.

/oh"leuh fin/, n. Chem.

any member of the alkene series.

Also, olefine /oh"leuh fin, -feen'/.

[1855-60; < F oléf(iant) (see OLEFIANT GAS) + -IN²]

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or alkene

Any unsaturated hydrocarbon containing one or more pairs of carbon atoms linked by a double bond (see covalent bond, saturation).

Olefins may be classified by whether the double bond is in a ring (cyclic) or a chain (acyclic, or aliphatic) or by the number of double bonds (monoolefin, diolefin, etc.). Rare in nature, olefins are obtained by the cracking of petroleum fractions at high temperatures. The simplest ones (ethylene, propylene, butylene, butadiene, and isoprene) are the basis of the petrochemicals industry. They react by adding other chemical agents at the double bond to form derivatives or polymers.

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▪ chemical compound

also called  alkene 

 any unsaturated hydrocarbon containing one or more pairs of carbon atoms linked by a double bond. The olefins 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 C_nH_2n1PT, C being a carbon atom, H a hydrogen atom, and n an integer. They are rare in nature but are formed in large quantities during the cracking (breaking down of large molecules) of petroleum oils to gasoline. The lower monoolefins—i.e., ethylene, propylene, and butylene—have become the basis for the extensive petrochemicals industry. Most uses of these compounds involve reactions of the double bond with other chemical agents. Acyclic diolefins, also known as acyclic dialkenes, or acyclic dienes, with the general formula C_nH_2n-2, contain two double bonds; they undergo reactions similar to the monoolefins. The best-known dienes are butadiene and isoprene, used in the manufacture of synthetic rubber.

      Olefins containing two to four carbon atoms per molecule are gaseous at ordinary temperatures and pressure; those containing five or more carbon atoms are usually liquid at ordinary temperatures. Olefins are only slightly soluble in water.

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