{{Short description|Alkyne with four carbon atoms}} {{chembox | verifiedrevid = 403365671 | Reference=<ref>[https://www.sigmaaldrich.com/US/en/product/aldrich/254339] at Sigma-Aldrich</ref><ref>[http://webbook.nist.gov/cgi/cbook.cgi?ID=C503173 NIST Chemistry WebBook page for 2-butyne]</ref> | Name = 2-Butyne | ImageFile1 = <chem>H3C-C#C-CH3</chem> | ImageSize1 = 180px | ImageName1 = Structural formula | ImageFile2 = 2-butyne-3D-balls-B.png | ImageSize2 = 150px | ImageName2 = Ball-and-stick model | ImageClass2 = bg-transparent | PIN = But-2-yne <!-- Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book) --> | OtherNames = Dimethylacetylene<br />Crotonylene |Section1={{Chembox Identifiers | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | ChemSpiderID = 9990 | PubChem = 10419 | ChEMBL_Ref = {{ebicite|correct|EBI}} | ChEMBL = 119108 | InChI = 1/C4H6/c1-3-4-2/h1-2H3 | InChIKey = XNMQEEKYCVKGBD-UHFFFAOYAO | StdInChI_Ref = {{stdinchicite|correct|chemspider}} | StdInChI = 1S/C4H6/c1-3-4-2/h1-2H3 | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} | StdInChIKey = XNMQEEKYCVKGBD-UHFFFAOYSA-N | CASNo_Ref = {{cascite|correct|CAS}} | CASNo = 503-17-3 | UNII_Ref = {{fdacite|correct|FDA}} | UNII = LKE6D3018E | SMILES = CC#CC }} |Section2={{Chembox Properties | C=4 | H=6 | Density = 0.691 g/mL | MeltingPtC = -32 | BoilingPtC = 27 }} }}
'''2-Butyne''' ('''dimethylacetylene''', '''crotonylene''' or '''but-2-yne''') is an alkyne with chemical formula CH<sub>3</sub>C≡CCH<sub>3</sub>. Produced artificially, it is a colorless, volatile, pungent liquid at standard temperature and pressure.
2-Butyne is of interest to physical chemists because of its very low torsional barrier and the problem of determining that barrier using high-resolution infrared spectroscopy. Analysis of its infrared spectrum<ref>{{cite journal | last = di Lauro | first = C.|display-authors=etal| year = 1997 | title =The rotation-torsion structure in the ν11/ν15 (Gs) methyl rocking fundamental band in dimethylacetylene | journal = J. Mol. Spectrosc.| volume = 184 | issue = 1 | pages = 177–185 | doi =10.1006/jmsp.1997.7321}}</ref> leads to a determination that the torsional barrier is only 6 cm<sup>−1</sup> (1.2{{e|-22}} J or 72 J mol<sup>−1</sup>). However, it has not been determined whether the equilibrium structure is eclipsed (D<sub>3h</sub>) or staggered (D<sub>3d</sub>). Symmetry analysis using the Molecular Symmetry Group<ref name=Longuet-Higgins1963>{{cite journal | last1 = Longuet-Higgins | first1 = H.C. | year = 1963 | title = The symmetry groups of non-rigid molecules | journal = Molecular Physics | volume = 6 | issue = 5| pages = 445–460 | doi = 10.1080/00268976300100501 | bibcode = 1963MolPh...6..445L | doi-access = free }}</ref><ref>{{cite journal | author1=P. R. Bunker | year=1964 | title=The Rotation-Torsion Wavefunctions of Molecules that have two Identical Rotors | journal=Mol. Phys. | volume=8 | page=81 | doi = 10.1080/00268976400100091}}</ref> G<sub>36</sub> shows that one would need to analyse its high resolution rotation-vibration Raman spectrum to determine its equilibrium structure. Pulsed-field-ionisation zero-kinetic-energy (PFI-ZEKE) photoelectron spectra of 2-butyne and its fully deuterated isotopomer have been recorded and analysed.<ref>{{cite journal | last = Jacovella | first = Ugo|display-authors=etal| year = 2015 | title=Internal rotation, spin–orbit coupling, and low-frequency vibrations in the ground state of CH3–CC–CH+3 and CD3–CC–CD+3 | journal=Mol. Phys. | volume=113 | page=2115 | doi = 10.1080/00268976.2015.1005708| hdl=20.500.11850/182812| hdl-access=free}}</ref>
2-Butyne (''dimethylethyne'') forms with 5-decyne (''dibutylethyne''), 4-octyne (''dipropylethyne'') and 3-hexyne (''diethylethyne'') a group of symmetric alkynes.
==Synthesis== 2-Butyne can be synthesized by the rearrangement reaction of ethylacetylene in a solution of ethanolic potassium hydroxide.<ref>{{cite book|author1=Victor von Richter |author2=Hans Meerwein|title=Organic Chemistry: Chemistry of the aliphatic series Vol. I: Smith's 3rd American Ed.|year=1916|publisher=P. Blakiston's Sons & Co.|location=Philadelphia|page=89|url=https://books.google.com/books?id=UWlZAAAAYAAJ&q=dimethylacetylene+preparation&pg=PA89}}</ref>
==Applications== 2-Butyne, along with propyne, is used to synthesize alkylated hydroquinones in the total synthesis of Vitamin E.<ref name=Cyclization>{{cite journal|author1=Reppe, Walter |author2=Kutepow, N |author3=Magin, A |title=Cyclization of Acetylenic Compounds|journal=Angewandte Chemie International Edition in English|year=1969|volume=8|issue=10|pages=727–733|doi=10.1002/anie.196907271}}</ref>
==See also== *Acetylenedicarboxylic acid *1-Butyne, a position isomer *1,4-Butynediol *Hexamethylbenzene, a product of 2-butyne trimerization *Hexafluoro-2-butyne
==References== {{reflist}}
{{Alkynes}}
{{DEFAULTSORT:Butyne, 2-}} Category:Alkynes