View source for Chemistry:Carbyne

{{Short description|Organic molecule containing a neutral carbon atom with 3 unpaired valence electrons}}
{{multiple image
|align = right
|direction = horizontal
|image1 = carbyne doublet.svg
|width1 = 100
|alt1 = carbyne doublet configuration
|caption1 = doublet (1 radical, 1 pair, 1 vacant orbital)
|image2 = carbyne quartet.svg
|width2 = 100
|alt2 = carbyne quartet configuration
|caption2 = quartet (3 radicals)
}}

In [[Chemistry:Organic chemistry|organic chemistry]], a '''carbyne''' is a general term for any [[Chemistry:Chemical compound|compound]] whose structure consists of an [[Physics:Electric charge|electrically neutral]] [[Chemistry:Carbon|carbon]] atom connected by a [[Chemistry:Single bond|single covalent bond]] and has three non-bonded electrons.<ref>{{goldbookref |title= carbynes |file= C00854 }}</ref> The carbon atom has either one or three unpaired [[Physics:Electron|electron]]s, depending on its [[Physics:Excited state|excitation state]]; making it a [[Biology:Radical|radical]]. The [[Chemistry:Chemical formula|chemical formula]] can be written {{chem2|R\sC*}} or {{chem2|R\sC^{3·} }} (also written as {{chem2|⫶C\sR}}), or just CH.

Carbynes can be seen as derivatives of the simplest such compound, the [[Chemistry:Methylidyne radical|methylidyne radical]] or unsubstituted carbyne {{chem2|H\sC*}} or {{chem2|H\sC^{3·} }}, in which the functional group is a [[Chemistry:Hydrogen|hydrogen]] atom.

Reported for the first time back in 1967 by Kasatochkin, carbyne is an infinite sp1 hybridized long linear chain of carbon, where each link is just a single carbon atom.<ref>{{Cite journal |last1=KASATOCHKIN |first1=VI |last2=VV |first2=KORSHAK |last3=YP |first3=KUDRYAVTSEV |last4=AM |first4=SLADKOV |last5=IE |first5=STERENBERG |date=1973 |title=ON CRYSTALLINE STRUCTURE OF CARBYNE |url=https://pascal-francis.inist.fr/vibad/index.php?action=getRecordDetail&idt=PASCAL7316105892 |journal=On Crystalline Structure of Carbyne}}</ref>

==Electronic configuration==
Carbyne molecules are generally found to be in electronic [[Physics:Doublet state|doublet state]]s: the non-bonding electrons on carbon are arranged as one [[Biology:Radical|radical]] (unpaired electron) and one electron pair, leaving a vacant [[Physics:Atomic orbital|atomic orbital]], rather than being a triradical (the quartet state). The simplest case is the CH radical, which has an [[Physics:Electron configuration|electron configuration]] {{nowrap|1σ<sup>2</sup> 2σ<sup>2</sup> 3σ<sup>2</sup> 1π}}.<ref name=Ruzsicska/> Here the 1σ [[Chemistry:Molecular orbital|molecular orbital]] is essentially the carbon 1s atomic orbital, and the 2σ is the C–H bonding orbital formed by [[Orbital overlap|overlap]] of a carbon sp [[Physics:Orbital hybridisation|hybrid orbital]] with the hydrogen 1s orbital. The 3σ is a carbon [[Chemistry:Non-bonding orbital|non-bonding orbital]] pointing along the C–H axis away from the hydrogen, while there are two non-bonding 1π orbitals perpendicular to the C–H axis. However the 3σ is an sp hybrid which has lower energy than the 1π orbital which is pure p, so the 3σ is filled before the 1π. The CH radical is in fact isoelectronic with the nitrogen atom which does have three unpaired electrons in accordance with [[Chemistry:Hund's rule of maximum multiplicity|Hund's rule of maximum multiplicity]]. However the nitrogen atom has three [[Physics:Degenerate energy levels|degenerate]] p orbitals, in contrast to the CH radical where hybridization of one orbital (the 3σ) leads to an energy difference.

==Occurrence==
A carbyne can occur as a short-lived [[Chemistry:Reactive intermediate|reactive intermediate]]. For instance, [[Chemistry:Fluoromethylidyne|fluoromethylidyne]] (CF) can be detected in the gas phase by spectroscopy as an intermediate in the [[Physics:Flash photolysis|flash photolysis]] of [[Chemistry:Dibromofluoromethane|CHFBr<sub>2</sub>]].<ref name=Ruzsicska>{{cite journal |author= Ruzsicska, B. P. |author2= Jodhan, A. |author3= Choi, H. K. J.|author4-link=Otto P. Strausz |author4= Strausz, O. P. |author5= Bell, T. N. |title= Chemistry of carbynes: reaction of CF, CCl, and CBr with alkenes |journal= J. Am. Chem. Soc. |volume= 105 |issue= 8 |year= 1983 |pages= 2489–2490 |doi= 10.1021/ja00346a072}}</ref>

Carbynes can act as trivalent [[Chemistry:Ligand|ligand]]s in [[Chemistry:Transition metal carbyne complex|complexes with transition metals]], in which they are connected to a [[Chemistry:Metal|metal]] by the three non-bonded electrons in the –C<sup>3•</sup> group. Examples of such coordination compounds are {{chem|Cl(CO)|4|W≡C-CH|3}},<ref>{{cite journal|doi=10.1002/anie.197305641|title=''trans''-Halogeno[alkyl(aryl)carbyne]tetracarbonyl Complexes of Chromium, Molybdenum, and Tungsten—A New Class of Compounds Having a Transition Metal-Carbon Triple Bond|journal=Angewandte Chemie International Edition in English|volume=12|issue=7|pages=564–565|year=1973|last1=Fischer|first1=Ernst Otto|last2=Kreis|first2=Gerhard|last3=Kreiter|first3=Cornelius G.|last4=Müller|first4=Jörn|last5=Huttner|first5=Gottfried|last6=Lorenz|first6=Hans}}</ref> [[Chemistry:Tungsten|W]][[Chemistry:Bromine|Br]](CO)<sub>2</sub>(2,2'-bipyridine)≡[[Chemistry:Carbon|C]]-[[Chemistry:Aryl|aryl]] and WBr(CO)<sub>2</sub>([[Chemistry:Triphenylphosphine|PPh<sub>3</sub>]])<sub>2</sub>≡C-NR<sub>2</sub>.<ref name=jaeg>{{cite journal |journal= Chem. Commun. |issue= 11 |title= Novel hepta-coordinated molybdenum(II) and tungsten(II) carbene complexes by oxidative decarbonylation of Mo(0) and W(0) carbene complexes |author1=Jaeger, M. |author2=Stumpf, R. |author3=Troll, C. |author4=Fischer, H. |year= 2000 |pages= 931–932 |doi= 10.1039/B002228O }}</ref> Such a compound can be obtained by the reaction of [[Chemistry:Tungsten hexacarbonyl|tungsten hexacarbonyl]] W(CO)<sub>6</sub> with [[Chemistry:Lithium diisopropylamide|lithium diisopropylamide]] to form (<sup>i</sup>Pr<sub>2</sub>N)(OLi)C=W(CO)<sub>5</sub>. This salt is then oxidized with either oxalyl bromide or triphenylphosphine dibromide, followed by addition of [[Chemistry:Triphenylphosphine|triphenylphosphine]]. Another method is to treat a methoxy metal [[Chemistry:Carbene|carbene]] with a [[Chemistry:Lewis acid|Lewis acid]].<ref name=jaeg/>

== References ==
{{Reflist}}


[[Category:Free radicals]]
[[Category:Organometallic chemistry]]

{{Sourceattribution|Carbyne}}