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 materials, i.e., matter in its various forms that contain carbon atoms.Clay ...

, polyenes are poly- unsaturated,

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon- hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...

s that contain at least three alternating

double A double is a look-alike or doppelgänger; one person or being that resembles another. Double, The Double or Dubble may also refer to: Film and television * Double (filmmaking), someone who substitutes for the credited actor of a character * Th ...

() and single () carbon–carbon bonds. These carbon–carbon double bonds interact in a process known as

conjugation Conjugation or conjugate may refer to: Linguistics *Grammatical conjugation, the modification of a verb from its basic form * Emotive conjugation or Russell's conjugation, the use of loaded language Mathematics *Complex conjugation, the change ...

, resulting in some unusual optical properties. Related to polyenes are dienes, where there are only two alternating double and single bonds. The following polyenes are used as

antibiotics An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention ...

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 Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiati ...

region of a

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of color ...

, 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 A chromophore is the part of a molecule responsible for its color. The color that is seen by our eyes is the one not absorbed by the reflecting object within a certain wavelength spectrum of visible light. The chromophore is a region in the molec ...

). 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 A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an ester derived from glycerol and three fatty acids (from ''tri-'' and '' glyceride''). Triglycerides are the main constituents of body fat in humans and other vertebrates, as ...

are reactive towards atmospheric oxygen.

Polyacetylene Polyacetylene (IUPAC name: polyethyne) usually refers to an organic polymer with the repeating unit . The name refers to its conceptual construction from polymerization of acetylene to give a chain with repeating olefin groups. This compound ...

, which partially oxidized or reduced, exhibits high electrical conductivity. Most

conductive polymer Conductive polymers or, more precisely, intrinsically conducting polymers (ICPs) are organic polymers that conduct electricity. Such compounds may have metallic conductivity or can be semiconductors. The biggest advantage of conductive polymer ...

s are polyenes, and many have conjugated structures. Poly(aza)acetylenes are readily prepared from

pyridine Pyridine is a basic (chemistry), basic heterocyclic compound, heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom. It is a highly flammable, weakl ...

precursors without the necessity of a controlled atmosphere, simply by

irradiation of a mixture of pyridine and poly(4-vinyl) pyridine. Recent research at the

Weizmann Institute The Weizmann Institute of Science ( he, מכון ויצמן למדע ''Machon Vaitzman LeMada'') is a public research university in Rehovot, Israel, established in 1934, 14 years before the State of Israel. It differs from other Israeli un ...

and

Aix-Marseille University Aix-Marseille University (AMU; french: Aix-Marseille Université; formally incorporated as ''Université d'Aix-Marseille'') is a public research university located in the Provence region of southern France. It was founded in 1409 when Louis II o ...

showed a clear transition between ionic and electronic conductivity with increasing UV dose over 30 hours.

Occurrence

A few

fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, ...

s are polyenes. Another class of important polyenes are polyene antimycotics, File:Amphotericin B new.svg, Amphotericin B is an example of a polyene antifungal (antimycotic) agent. File:Leukotriene A4.svg,

Leukotriene Leukotrienes are a family of eicosanoid inflammatory mediators produced in leukocytes by the oxidation of arachidonic acid (AA) and the essential fatty acid eicosapentaenoic acid (EPA) by the enzyme arachidonate 5-lipoxygenase. Leukotrie ...

A4 is a regulator of the immune response. File:Trans-Polyacetylene.svg,

s are a synthetic polymer of theoretical interest because they exhibit metallic properties upon oxidation.Lam, Jacky W. Y.; Tang, Ben Zhong "Functional Polyacetylenes" Accounts of Chemical Research 2005, volume 38, pp. 745-754.

References

{{reflist Polyenes Conjugated hydrocarbons