View source for Alkyne

{{short description|Hydrocarbon compound containing one or more C≡C bonds}}
{{distinguish|alkane|alkene}}
<div style="float:right; border:1px solid grey; padding:1em;">
<math chem>\ce{H-C#C}
\ce{-H}</math>
<div>[[Acetylene]]</div>
<math chem>\ce{H-C#C}{-}
\ce{\overset{\displaystyle{H} \atop |}{\underset{| \atop \displaystyle{H}}C}}
\ce{-H}</math>
<div>[[Propyne]]</div>
<math chem>\ce{H-C#C}{-}
\ce{\overset{\displaystyle{H} \atop |}{\underset{| \atop \displaystyle{H}}C}}{-}
\ce{\overset{\displaystyle{H} \atop |}{\underset{| \atop \displaystyle{H}}C}}
\ce{-H}</math>
<div>[[1-Butyne]]</div>
</div>

[[File:Acetylene-3D-vdW.png|right|thumb|A 3D model of ethyne ([[acetylene]]), the simplest alkyne]]

In [[organic chemistry]], an '''alkyne''' is an [[Saturated and unsaturated compounds|unsaturated]] [[hydrocarbon]] containing at least one [[carbon]]—carbon [[triple bond]].<ref>[https://www.britannica.com/EBchecked/topic/15818/alkyne Alkyne]. Encyclopædia Britannica</ref> The simplest [[Open-chain compound|acyclic]] alkynes with only one triple bond and no other [[functional group]]s form a [[homologous series]] with the general chemical formula  {{chem2|C_{''n''}H_{2''n''-2} }}. Alkynes are traditionally known as acetylenes, although the name ''acetylene'' also refers specifically to {{chem2|C2H2}}, known formally as [[ethyne]] using [[IUPAC nomenclature of organic chemistry|IUPAC nomenclature]]. Like other hydrocarbons, alkynes are generally [[hydrophobic]].<ref>{{cite book |title=The Carbon–Carbon Triple Bond|year=1978|isbn=9780470771563|publisher=John Wiley & Sons|editor=Saul Patai|volume=1}}</ref>

==Structure and bonding==
In acetylene, the H–C≡C [[bond angle]]s are 180°. By virtue of this bond angle, alkynes are rod-like. Correspondingly, cyclic alkynes are rare. [[Benzyne]] cannot be isolated. The C≡C bond distance of 118 [[picometer]]s (for C<sub>2</sub>H<sub>2</sub>) is much shorter than the C=C distance in [[alkene]]s (132&nbsp;pm, for C<sub>2</sub>H<sub>4</sub>) or the C–C bond in alkanes (153&nbsp;pm).<ref>{{cite book |doi=10.1002/0470084960|title=March's Advanced Organic Chemistry: Reactions, Mechanisms, and Structure |year=2006 |last1=Smith |first1=Michael B. |last2=March |first2=Jerry |isbn=9780470084960|page = 24 }}</ref>

:[[File:Alkyne General Formulae V.2.png|thumb|center|580px|Illustrative alkynes: '''a''', acetylene, '''b''', two depictions of propyne, '''c''', 1-butyne, '''d''', [[2-butyne]], '''e''', the naturally occurring 1-phenylhepta-1,3,5-triyne, and '''f''', the strained cycloheptyne. Triple bonds are highlighted <span style="color:blue;">'''blue'''</span>.]]

The [[triple bond]] is very strong with a [[bond strength]] of 839 kJ/mol. The [[sigma bond]] contributes 369&nbsp;kJ/mol, the first [[pi bond]] contributes 268&nbsp;kJ/mol. and the second pi bond 202&nbsp;kJ/mol. Bonding is usually discussed in the context of [[molecular orbital theory]], which recognizes the triple bond as arising from overlap of s and p orbitals. In the language of [[valence bond theory]], the carbon atoms in an alkyne bond are [[sp hybridized]]: they each have two unhybridized [[p orbital]]s and two [[Orbital hybridisation|sp hybrid orbitals]]. Overlap of an sp orbital from each atom forms one sp–sp [[sigma bond]]. Each p orbital on one atom overlaps one on the other atom, forming two pi bonds, giving a total of three bonds. The remaining sp orbital on each atom can form a sigma bond to another atom, for example to hydrogen atoms in the parent acetylene. The two sp orbitals project on opposite sides of the carbon atom.

===Terminal and internal alkynes===
Internal alkynes feature carbon substituents on each acetylenic carbon. Symmetrical examples include [[diphenylacetylene]] and [[3-hexyne]]. They may also be asymmetrical, such as in [[2-pentyne]].

Terminal alkynes have the formula {{chem2|RC≡CH}}, where at least one end of the alkyne is a hydrogen atom. An example is [[methylacetylene]] (propyne using IUPAC nomenclature).  They are often prepared by alkylation of [[monosodium acetylide]].<ref>{{cite journal |doi=10.15227/orgsyn.030.0015 |title=''n''-Butylacetylene |journal=Organic Syntheses |date=1950 |volume=30 |page=15|author=K. N. Campbell, B. K. Campbell }}</ref> Terminal alkynes, like [[acetylene]] itself, are mildly acidic, with p''K''<sub>a</sub> values of around 25. They are far more acidic than alkenes and alkanes, which have p''K''<sub>a</sub> values of around 40 and 50, respectively. The acidic hydrogen on terminal alkynes can be replaced by a variety of groups resulting in halo-, silyl-, and alkoxoalkynes. The [[carbanion]]s generated by deprotonation of terminal alkynes are called [[acetylide]]s.<ref name="de57">{{cite book|last=Bloch|first=Daniel R.|title=Organic Chemistry Demystified|year=2012|publisher=McGraw-Hill|isbn=978-0-07-176797-2|pages=57|edition=2nd}}</ref> Internal alkynes are also considerably more acidic than alkenes and alkanes, though not nearly as acidic as terminal alkynes.  The C–H bonds at the α position of alkynes (propargylic C–H bonds) can also be deprotonated using strong bases, with an estimated p''K''<sub>a</sub> of 35.  This acidity can be used to isomerize internal alkynes to terminal alkynes using the [[alkyne zipper reaction]].

==Naming alkynes==
In [[Chemical nomenclature|systematic chemical nomenclature]], alkynes are named with the Greek prefix system without any additional letters. Examples include ethyne or octyne. In parent chains with four or more carbons, it is necessary to say where the triple bond is located. For [[octyne]], one can either write 3-octyne or oct-3-yne when the bond starts at the third carbon. The lowest number possible is given to the [[triple bond]]. When no superior functional groups are present, the parent chain must include the triple bond even if it is not the longest possible carbon chain in the molecule. Ethyne is commonly called by its trivial name acetylene.

In chemistry, the [[affix|suffix]] '''[[-yne]]''' is used to denote the presence of a triple bond. In [[organic chemistry]], the suffix often follows [[Chemical nomenclature|IUPAC nomenclature]]. However, [[inorganic compound]]s featuring [[Saturated and unsaturated compounds|unsaturation]] in the form of triple bonds may be denoted by substitutive nomenclature with the same methods used with alkynes (i.e. the name of the corresponding saturated compound is modified by replacing the "[[-ane]]" ending with "-yne"). "[[Polyyne|-diyne]]" is used when there are two triple bonds, and so on. The position of unsaturation is indicated by a numerical [[locant]] immediately preceding the "-yne" suffix, or 'locants' in the case of multiple triple bonds. Locants are chosen so that the numbers are low as possible. "-yne" is also used as a suffix to name substituent groups that are triply bound to the parent compound.

Sometimes a number between [[hyphen]]s is inserted before it to state which atoms the triple bond is between. This suffix arose as a collapsed form of the end of the word "[[acetylene]]". The final "-e" disappears if it is followed by another suffix that starts with a vowel.<ref>{{Cite book |author=The Commission on the Nomenclature of Organic Chemistry |title=Nomenclature of Organic Chemistry |orig-year= 1958 (A: Hydrocarbons, and B: Fundamental Heterocyclic Systems), 1965 (C: Characteristic Groups) |year=1971 |edition=3rd |publisher=Butterworths |location=London |isbn= 0-408-70144-7}}</ref>

== Structural isomerism ==
Alkynes having four or more [[carbon]] atoms can form different [[structural isomer]]s by having the triple bond in different positions or having some of the carbon atoms be substituents rather than part of the parent chain. Other non-alkyne structural isomers are also possible.
* {{Chem2|C2H2}}: [[acetylene]] only
* {{Chem2|C3H4}}: [[propyne]] only
* {{Chem2|C4H6}}: 2 isomers: [[1-butyne]], and [[2-butyne]] 
* {{Chem2|C5H8}}: 3 isomers: [[1-pentyne]], [[2-pentyne]], and 3-methyl-1-butyne
* {{Chem2|C6H10}}: 7 isomers: [[1-hexyne]], 2-hexyne, [[3-hexyne]], 4-methyl-1-pentyne, 4-methyl-2-pentyne, 3-methyl-1-pentyne, 3,3-dimethyl-1-butyne

==Synthesis==

=== From calcium carbide ===
Classically, acetylene was prepared by hydrolysis (protonation) of [[calcium carbide]] (Ca<sup>2+</sup>[:C≡C:]<sup>2–</sup>):
:<chem>Ca^{2+}[C#C]^2- + 2 HOH -> HC#CH + Ca^{2+}[(HO^{-})2]</chem>
which was in turn synthesized by combining [[Calcium oxide|quicklime]] and [[Coke (fuel)|coke]] in an [[electric arc furnace]] at 2200 °C:

: <chem>CaO + 3 C (amorphous) ->  CaC2 + CO</chem>

This was an industrially important process which provided access to hydrocarbons from coal resources for countries like Germany and China.  However, the energy-intensive nature of this process is a major disadvantage and its share of the world's production of acetylene has steadily decreased relative to hydrocarbon cracking.<ref>{{Cite journal |last=Trotuş |first=Ioan-Teodor |last2=Zimmermann |first2=Tobias |last3=Schüth |first3=Ferdi |date=2014-02-12 |title=Catalytic Reactions of Acetylene: A Feedstock for the Chemical Industry Revisited |url=https://pubs.acs.org/doi/10.1021/cr400357r |journal=Chemical Reviews |volume=114 |issue=3 |pages=1761–1782 |doi=10.1021/cr400357r |issn=0009-2665}}</ref>

===Cracking===
Commercially, the dominant alkyne is acetylene itself, which is used as a fuel and a precursor to other compounds, e.g., [[acrylate]]s. Hundreds of millions of kilograms are produced annually by [[partial oxidation]] of [[natural gas]]:<ref name=Ullmann/>
: <chem>2 CH4 + 3/2 O2 -> HC#CH + 3 H2O</chem>
Propyne, also industrially useful, is also prepared by [[thermal cracking]] of hydrocarbons. 

=== Alkylation and arylation of terminal alkynes ===
Terminal alkynes (RC≡CH, including acetylene itself) can be deprotonated by bases like [[Sodium amide|NaNH<sub>2</sub>]], [[N-Butyllithium|BuLi]], or [[Ethylmagnesium bromide|EtMgBr]] to give [[acetylide]] anions (RC≡C:<sup>–</sup>M<sup>+</sup>, M = Na, Li, MgBr) which can be alkylated by addition to carbonyl groups ([[Favorskii reaction]]), ring opening of epoxides, or S<sub>N</sub>2-type substitution of unhindered primary alkyl halides.  

In the presence of transition metal catalysts, classically a combination of [[Bis(triphenylphosphine)palladium chloride|Pd(PPh<sub>3</sub>)<sub>2</sub>Cl<sub>2</sub>]] and [[Copper(I) iodide|CuI]], terminal acetylenes (RC≡CH) can react with aryl iodides and bromides (ArI or ArBr) in the presence of a secondary or tertiary amine like [[Triethylamine|Et<sub>3</sub>N]] to give arylacetylenes (RC≡CAr) in the [[Sonogashira reaction]].

The availability of these reliable reactions makes terminal alkynes useful building blocks for preparing internal alkynes.

===Dehydrohalogenation and related reactions===
Alkynes are prepared from 1,1- and 1,2-[[dihaloalkane]]s by double [[dehydrohalogenation]]. The reaction provides a means to generate alkynes from alkenes, which are first [[halogenated]] and then dehydrohalogenated. For example, [[phenylacetylene]] can be generated from [[styrene]] by [[bromination]] followed by treatment of the resulting of 1,2-dibromo-1-phenylethane with [[sodium amide]] in [[ammonia]]:<ref>{{OrgSynth | doi= 10.15227/orgsyn.030.0072| volume= 30 | page = 72 | year = 1950 | title = Phenylacetylene | author = Kenneth N. Campbell, Barbara K. Campbell}}</ref><ref>{{cite journal |doi=10.15227/orgsyn.059.0010|title=Alkyness via Phase Transfer-Catalyzed Dehydrohalogenatiion: Propiolaldehyde Diethyl Acetal|journal=Organic Syntheses|year=1979|volume=59|page=10|author=A. Le Coq and A. Gorgues}}</ref>

:[[File:Phenylacetylene prepn.png|350px]]

Via the [[Fritsch–Buttenberg–Wiechell rearrangement]], alkynes are prepared from [[vinyl bromide]]s. Alkynes can be prepared from [[aldehyde]]s using the [[Corey–Fuchs reaction]] and from aldehydes or [[ketone]]s by the [[Seyferth–Gilbert homologation]].  

[[Vinyl halide]]s are susceptible to dehydrohalogenation.

==Reactions, including applications==
Featuring a reactive [[functional group]], alkynes participate in many [[organic reaction]]s. Such use was pioneered by [[Ralph Raphael]], who in 1955 wrote the first book describing their versatility as intermediates in [[organic synthesis|synthesis]].<ref>{{cite book |author=Raphael, Ralph Alexander | title =Acetylenic compounds in organic synthesis | year =1955 | publisher= Butterworths Scientific Publications  |location=London |url= https://babel.hathitrust.org/cgi/pt?id=mdp.39015064396958;view=1up;seq=12 |oclc=3134811}}</ref>  In spite of their kinetic stability (persistence) due to their strong triple bonds, alkynes are a thermodynamically unstable functional group, as can be gleaned from the highly positive heats of formation of small alkynes.  For example, acetylene has a heat of formation of +227.4 kJ/mol (+54.2 kcal/mol), indicating a much higher energy content compared to its constituent elements.  The highly exothermic combustion of acetylene is exploited industrially in oxyacetylene torches used in welding.  Other reactions involving alkynes are often highly thermodynamically favorable (exothermic/exergonic) for the same reason.

===Hydrogenation===
Being more [[Saturated and unsaturated compounds|unsaturated]] than alkenes, alkynes characteristically undergo reactions that show that they are "doubly unsaturated". Alkynes are capable of adding two equivalents of {{chem2|H2}}, whereas an alkene adds only one equivalent.<ref>{{cite book|author=Rosser|author2=Williams|name-list-style=amp|title=Modern Organic Chemistry for A-level|year=1977|publisher=Collins|location=Great Britain|isbn=0003277402|page=82}}</ref> Depending on catalysts and conditions, alkynes add one or two equivalents of hydrogen. Partial [[hydrogenation]], stopping after the addition of only one equivalent to give the [[alkene]], is usually more desirable since alkanes are less useful:
[[File:PhC2HH2.png|frameless|400px|center]]
The largest scale application of this technology is the conversion of acetylene to ethylene in refineries (the steam cracking of alkanes yields a few percent acetylene, which is selectively hydrogenated in the presence of a [[palladium]]/[[silver]] catalyst). For more complex alkynes, the [[Lindlar catalyst]] is widely recommended to avoid formation of the alkane, for example in the conversion of [[phenylacetylene]] to [[styrene]].<ref>{{OrgSynth | collvol = 5 | collvolpages = 880 | year = 1973 | prep = cv5p0880 | author = H. Lindlar |author2=R. Dubuis | title = Palladium catalyst for partial reduction of acetylenes}}.</ref> Similarly, [[halogenation]] of alkynes gives the alkene dihalides or alkyl tetrahalides:

:<math chem>\ce{RC#CR' + H2 ->} \text{ cis-}\ce{RCH=CR'H}</math>
:<chem>RCH=CR'H + H2 -> RCH2CR'H2</chem>

The addition of one equivalent of {{chem2|H2}} to internal alkynes gives cis-alkenes.

===Addition of halogens and related reagents===
Alkynes characteristically are capable of adding two equivalents of [[halogen]]s and hydrogen halides. 
:<chem>RC#CR' + 2 Br2 -> RCBr2CR'Br2</chem>

The addition of nonpolar {{chem2|E\sH}} bonds across {{chem2|C\tC}} is general for silanes, boranes, and related hydrides. The [[hydroboration-oxidation reaction|hydroboration]] of alkynes gives vinylic boranes which oxidize to the corresponding [[aldehyde]] or ketone. In the [[thiol-yne reaction]] the substrate is a thiol.

Addition of hydrogen halides has long been of interest. In the presence of [[mercuric chloride]] as a [[catalyst]], acetylene and [[hydrogen chloride]] react to give [[vinyl chloride]]. While this method has been abandoned in the West, it remains the main production method in China.<ref name=UllmannVC>{{Ullmann|doi=10.1002/14356007.o06_o01|title=Chlorethanes and Chloroethylenes|year=2011|last1=Dreher|first1=Eberhard-Ludwig|last2=Torkelson|first2=Theodore R.|last3=Beutel|first3=Klaus K.|isbn=978-3527306732}}</ref>

===Hydration===
The [[hydration reaction]] of acetylene gives [[acetaldehyde]].  The reaction proceeds by formation of [[vinyl alcohol]], which [[Keto–enol tautomerism|tautomerize]]s to form the aldehyde. This reaction was once a major industrial process but it has been displaced by the [[Wacker process]]. This reaction occurs in nature, the catalyst being [[acetylene hydratase]].

Hydration of [[phenylacetylene]] gives [[acetophenone]]:<ref>{{cite journal |author1=Fukuda, Y. |author2=Utimoto, K. | title = Effective transformation of unactivated alkynes into ketones or acetals with a gold(III) catalyst | journal = [[J. Org. Chem.]] | doi = 10.1021/jo00011a058 | year = 1991 | volume = 56 | pages = 3729 | issue = 11}}</ref>
:<chem>PhC#CH + H2O -> PhCOCH3</chem>
[[Methyl(triphenylphosphine)gold(I)|{{chem2|(Ph3P)AuCH3}}]] catalyzes hydration of 1,8-nonadiyne to 2,8-nonanedione:<ref>{{OrgSynth | author = Mizushima, E. |author2=Cui, D.-M. |author3=Nath, D. C. D. |author4=Hayashi, T. |author5=Tanaka, M. | title = Au(I)-Catalyzed hydratation of alkynes: 2,8-nonanedione | volume = 83 | pages = 55 | year = 2005 | prep = v83p0055}}</ref>
:<chem>HC#C(CH2)5C#CH + 2H2O -> CH3CO(CH2)5COCH3</chem>

===Isomerization to allenes===
Alkynes can be isomerized by strong base or transition metals to [[allenes]].  Due to their comparable thermodynamic stabilities, the equilibrium constant of alkyne/allene isomerization is generally within several orders of magnitude of unity.  For example [[propyne]] can be isomerized to give an equilibrium mixture with [[propadiene]]:
:<chem>HC#C-CH3 <=> CH2=C=CH2</chem>

===Cycloadditions and oxidation===
Alkynes undergo diverse [[cycloaddition]] reactions. The [[Diels–Alder reaction]] with 1,3-[[diene]]s gives [[1,4-cyclohexadienes]]. This general reaction has been extensively developed. Electrophilic alkynes are especially effective [[dienophile]]s. The "cycloadduct" derived from the addition of alkynes to [[2-pyrone]] eliminates [[carbon dioxide]] to give the [[aromatic]] compound. Other specialized cycloadditions include multicomponent reactions such as [[alkyne trimerisation]] to give [[aromatic]] compounds and the [2+2+1]-cycloaddition of an alkyne, [[alkene]] and [[carbon monoxide]] in the [[Pauson–Khand reaction]]. Non-carbon reagents also undergo cyclization, e.g. [[azide alkyne Huisgen cycloaddition]] to give [[triazole]]s. Cycloaddition processes involving alkynes are often catalyzed by metals, e.g. [[enyne metathesis]] and [[alkyne metathesis]], which allows the scrambling of [[carbyne]] (RC) centers:
:<chem>RC#CR + R'C#CR' <=> 2RC#CR'</chem>
Oxidative cleavage of alkynes proceeds via cycloaddition to metal oxides. Most famously, [[potassium permanganate]] converts alkynes to a pair of [[carboxylic acid]]s.

===Reactions specific for terminal alkynes===
Terminal alkynes are readily converted to many derivatives, e.g. by coupling reactions and condensations.  Via the condensation with formaldehyde and acetylene is produced [[1,4-Butynediol|butynediol]]:<ref name="Ullmann">{{Ullmann|first1=Heinz|last1=Gräfje|first2=Wolfgang|last2=Körnig|first3=Hans-Martin|last3=Weitz|first4=Wolfgang|last4=Reiß|first5=Guido|last5=Steffan|first6=Herbert|last6=Diehl|first7=Horst |last7=Bosche|first8=Kurt|last8=Schneider|first9=Heinz|last9=Kieczka|title=Butanediols, Butenediol, and Butynediol|year=2000|doi=10.1002/14356007.a04_455}}</ref><ref name=UllmannC4>{{Ullmann |author1=Peter Pässler |author2=Werner Hefner |author3=Klaus Buckl |author4=Helmut Meinass |author5=Andreas Meiswinkel |author6=Hans-Jürgen Wernicke |author7=Günter Ebersberg |author8=Richard Müller |author9=Jürgen Bässler |author10=Hartmut Behringer |author11=Dieter Mayer |title=Acetylene | year=2008 |doi=10.1002/14356007.a01_097.pub3 }}</ref>  
:<chem>2CH2O + HC#CH  ->  HOCH2CCCH2OH</chem>

In the [[Sonogashira reaction]], terminal alkynes are coupled with aryl or vinyl halides:
:[[File:Sonogashira reaction scheme ACS.png|400px|The Sonogashira Reaction]]

This reactivity exploits the fact that terminal alkynes are weak acids, whose typical [[Acid dissociation constant|p''K''<sub>a</sub>]] values around 25 place them between that of [[ammonia]] (35) and [[ethanol]] (16):
:<chem>RC#CH + MX -> RC#CM + HX</chem>
where MX = [[sodium amide|NaNH<sub>2</sub>]], [[N-Butyllithium|LiBu]], or [[Grignard reagent|RMgX]].

The reactions of alkynes with certain metal cations, e.g. {{chem2|Ag+}} and {{chem2|Cu+}} also gives acetylides. Thus, few drops of [[Tollens reagent|diamminesilver(I) hydroxide]] ({{chem2|Ag(NH3)2OH}}) reacts with terminal alkynes signaled by formation of a white precipitate of the silver acetylide.  This reactivity is the basis of alkyne [[coupling reaction]]s, including the [[Cadiot–Chodkiewicz coupling]], [[Glaser coupling]], and the [[Eglinton coupling]] shown below:<ref>{{OrgSynth | title = <nowiki>[18]Annulene</nowiki> | author = K. Stöckel and F. Sondheimer | volume= 54 | page = 1| year = 1974 | doi= 10.15227/orgsyn.054.0001}}</ref> 

:<chem>2R-\!{\equiv}\!-H ->[\ce{Cu(OAc)2}][\ce{pyridine}] R-\!{\equiv}\!-\!{\equiv}\!-R</chem>

In the [[Favorskii reaction]] and in [[alkynylation]]s in general, terminal alkynes add to [[carbonyl]] compounds to give the [[hydroxyalkyne]].

===Metal complexes===
{{main|Transition metal alkyne complex}}
Alkynes form complexes with transition metals. Such complexes occur also in metal catalyzed reactions of alkynes such as [[alkyne trimerization]].  Terminal alkynes, including acetylene itself, react with water to give aldehydes.  The transformation typically requires metal catalysts to give this anti-Markovnikov addition result.<ref>{{cite journal|doi=10.1055/s-2007-966002|title=Catalytic Hydration of Alkynes and Its Application in Synthesis|journal=Synthesis|volume=2007|issue=8|pages=1121–1150|year=2007|last1=Hintermann|first1=Lukas|last2=Labonne|first2=Aurélie|s2cid=95666091}}</ref>

==Alkynes in nature and medicine==
According to [[Ferdinand Bohlmann]], the first naturally occurring acetylenic compound, dehydromatricaria ester, was isolated from an ''[[Artemisia (plant)|Artemisia]]'' species in 1826. In the nearly two centuries that have followed, well over a thousand naturally occurring acetylenes have been discovered and reported. [[Polyyne]]s, a subset of this class of natural products, have been isolated from a wide variety of plant species, cultures of higher fungi, bacteria, marine sponges, and corals.<ref>{{cite journal | author = Annabelle L. K. Shi Shun |author2=Rik R. Tykwinski| title = Synthesis of Naturally Occurring Polyynes| journal = Angew. Chem. Int. Ed. | year = 2006| volume = 45 | pages = 1034–1057| doi = 10.1002/anie.200502071 | issue = 7 | pmid=16447152}}</ref> Some acids like [[tariric acid]] contain an alkyne group. Diynes and triynes, species with the linkage RC≡C–C≡CR′ and RC≡C–C≡C–C≡CR′ respectively, occur in certain plants (''[[Ichthyothere]]'', ''[[Chrysanthemum]]'', ''[[Cicuta]]'', ''[[Oenanthe (plant)|Oenanthe]]'' and other members of the [[Asteraceae]] and [[Apiaceae]] families). Some examples are [[cicutoxin]], [[oenanthotoxin]], and [[falcarinol]]. These compounds are highly bioactive, e.g. as [[nematocide]]s.<ref>{{cite book |author =Lam, Jørgen |title=Chemistry and biology of naturally-occurring acetylenes and related compounds (NOARC): proceedings of a Conference on the Chemistry and Biology of Naturally-Occurring Acetylenes and Related Compounds (NOARC) |publisher=Elsevier |location=Amsterdam |year=1988 |isbn=0-444-87115-2 }}</ref> 1-Phenylhepta-1,3,5-triyne is illustrative of a naturally occurring triyne.  Biosynthetically, the [[enediyne]] natural products are also derived from a polyyne precursor.

Alkynes occur in some pharmaceuticals, including the contraceptive [[noretynodrel]]. A carbon–carbon triple bond is also present in marketed drugs such as the antiretroviral [[efavirenz]] and the antifungal [[terbinafine]]. Molecules called ene-diynes feature a ring containing an alkene ("ene") between two alkyne groups ("diyne"). These compounds, e.g. [[calicheamicin]], are some of the most aggressive antitumor drugs known, so much so that the ene-diyne subunit is sometimes referred to as a "warhead". Ene-diynes undergo rearrangement via the [[Bergman cyclization]], generating highly reactive radical intermediates that attack DNA within the tumor.<ref>{{cite journal |author1=S. Walker |author2=R. Landovitz |author3=W.D. Ding |author4=G.A. Ellestad |author5=D. Kahne | title = Cleavage behavior of calicheamicin gamma 1 and calicheamicin T | journal = Proc Natl Acad Sci USA | year = 1992| volume = 89 | issue = 10 | pages = 4608–12 | pmc=49132 | doi = 10.1073/pnas.89.10.4608 | pmid = 1584797|bibcode = 1992PNAS...89.4608W |doi-access=free }}</ref>

==See also==
{{wiktionary}}
{{wikiquote}}
* [[-yne]]
* [[cycloalkyne]]

==References==
{{Reflist}}

{{Hydrocarbons}}
{{Alkynes}}
{{Functional Groups}}
{{BranchesofChemistry}}

{{Authority control}}

[[Category:Alkynes| ]]