In
organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic matter, organic materials, i.e., matter in its various forms that contain ...
, polyenes are
polyunsaturated
In biochemistry and nutrition, a polyunsaturated fat is a fat that contains a polyunsaturated fatty acid (abbreviated PUFA), which is a subclass of fatty acid characterized by a backbone with two or more carbon–carbon double bonds.
Some polyunsa ...
organic compound
Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...
s that contain multiple
carbon–carbon double bond
In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betw ...
s ().
Some sources consider
diene
In organic chemistry, a diene ( ); also diolefin, ) or alkadiene) is a covalent compound that contains two double bonds, usually among carbon atoms. They thus contain two alk''ene'' units, with the standard prefix ''di'' of systematic nome ...
s to be polyenes, whereas others require polyenes to contain at least three carbon–carbon double bonds.
Conjugated polyenes contain a conjugated system of alternating single and double carbon–carbon bonds, with characteristic optical properties.
The following polyenes are used as antimycotics for humans: amphotericin B, nystatin, candicidin, pimaricin, methyl partricin, and trichomycin.
Optical properties
Some polyenes are brightly colored, an otherwise rare property for a hydrocarbon. Normally alkenes absorb in the ultraviolet region of a Ultraviolet-visible spectroscopy, spectrum, but the absorption energy state of polyenes with numerous conjugated double bonds can be lowered such that they enter the visible region of the spectrum, resulting in compounds which are coloured (because they contain a chromophore). Thus many natural dyes contain linear polyenes.
Chemical and electrical properties
Polyenes tend to be more reactive than simpler alkenes. For example, polyene-containing triglycerides are reactive towards atmospheric oxygen. Polyacetylene, which partially oxidized or reduced, exhibits high electrical conductivity. Most conductive polymers are polyenes, and many have conjugated system, conjugated structures. Poly(aza)acetylenes are readily prepared from pyridine precursors without the necessity of a controlled atmosphere, simply by ultraviolet irradiation of a mixture of pyridine and poly(4-vinyl) pyridine. Recent research at the Weizmann Institute of Science, Weizmann Institute and Aix-Marseille University showed a clear transition between ionic and electronic conductivity with increasing UV dose over 30 hours.
Occurrence
A few fatty acids are polyenes. Another class of important polyenes are polyene antimycotics.
[Lam, Jacky W. Y.; Tang, Ben Zhong. "Functional Polyacetylenes", Accounts of Chemical Research, 2005, volume 38, pp. 745–754. .]
References
{{Authority control
Polyenes,
Conjugated hydrocarbons