Isomers of butylene
Butene, also known as butylene, is an alkene with the formula C4H8. It is a colourless gas that is present in crude oil as a minor constituent in quantities that are too small for viable extraction. It is therefore obtained by catalytic cracking of long-chain hydrocarbons left during refining of crude oil. Cracking produces a mixture of products, and the butene is extracted from this by fractional distillation.
Butene can be used as the monomer for polybutene but this polymer is more expensive than alternatives with shorter carbon chains such as polypropylene. Polybutene is therefore commonly used as a co-polymer (mixed with another polymer, either during or after reaction), such as in hot-melt adhesives.
Among the molecules which have the chemical formula C4H8 four isomers are alkenes. All four of these hydrocarbons have four carbon atoms and one double bond in their molecules, but have different chemical structures. The IUPAC and common names, respectively, of these chemical compounds are:
In the chemical structures above, the small blue numbers in the structure images are the numbering of the atoms in the main backbone chain of the molecules. Other organic compounds have the formula C4H8, namely cyclobutane and methylcyclopropane, but are not alkenes and are not discussed here. There are also cyclic alkenes with four carbon atoms overall such as cyclobutene and two isomers of methylcyclopropene, but they do not have the formula C4H8 and are not discussed here.
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