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The nylon-making plant

at Flixborough, England, was devastated in 1974. Cy­clohexane exploded as it was being oxidized (one stage in the synthesis of nylon 6). Like other alkanes, cyclohexane can be oxi­dized completely to carbon dioxide and water. Such a reaction releases a large amount of energy if it is not controlled.


     
 
 
   


 

Ethene (ethylene, C2H4) Propene (propylene, C3H6)   PropadieneiCjH,,)
c = c H\ ! /H H—C —C = C   c=c=c
l-butene(C4H8) c/s-2-butene (C4HS) 1,3-butadiene(C4H6)
\ 1 T / H—C—C—C=C \ i T /H H-C—C=C—C-H   H H ^ H H\ 1 1 /
rrans-2-butene (C„H8) 2-methylbutene (C4H8)   1.2-butadiene(C4H.,)
H\ " /" H — C—C=C—C—H H /H H—C—C=C,/ 1, XH   C=C=C—C —H
Alkenesare unsaturated al­iphatic hydrocarbons with one carbon-carbon double bond. The first few mem­bers of the series are illus­trated {above left). Ethene (pink box) and propene (pale blue box) each have only one possible structure. However, butene has four (pale green panels). Alka-dienes have two carbon-car­bon double bonds. The first few members are illustrated above right. Propadiene (grey box) has only one pos­sible form, whereas butadi­ene (dark green box) has two.

Unsaturated

Aliphatic

Hydrocarbons

Unsaturated aliphatic hydrocarbons are the building blocks of the organic chemical indus­try. The term "unsaturated" indicates that the carbon atoms are not saturated (filled) with the maximum number of hydrogen atoms. Four bonds are possible for each carbon atom. Sat­urated hydrocarbons bond with four other atoms (a combination of carbon and hydrogen


atoms). Unsaturated hydrocarbons contain at least one carbon-carbon multiple bond. A double bond leaves room for only two other bonds with hydrogen or carbon. A triple bond makes possible only one other bond with hy­drogen or carbon.

Compounds with double bonds are also commonly known as alkenes or olefins. By far, the most important alkene is ethene (ethylene), followed by propene (propylene), and butadi­ene. Ethyne (acetylene) is the most important alkyne, as compounds with a triple carbon-car­bon bond are called.

Compounds with two or more multiple bonds are termed polyunsaturated (a charac­teristic of many natural fats and oils). Where there are two double bonds in an alkene, they may be differently arranged. The color of many organic compounds depends on the ar­rangement of double bonds in the molecule.

Date: 2015-12-11; view: 1785

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