2-Butyne

2-Butyne (dimethylacetylene, crotonylene or but-2-yne) is an alkyne with chemical formula CH3C≡CCH3. Produced artificially, it is a colorless, volatile, pungent liquid at standard temperature and pressure.

Names Identifiers ${\displaystyle {\ce {H3C-C#C-CH3}}}$ Preferred IUPAC name But-2-yne Other names DimethylacetyleneCrotonylene CAS Number 503-17-3 3D model (JSmol) Interactive image ChEMBL ChEMBL119108 ChemSpider 9990 ECHA InfoCard 100.007.239 PubChem CID 10419 UNII LKE6D3018E CompTox Dashboard (EPA) InChI InChI=1S/C4H6/c1-3-4-2/h1-2H3 Key: XNMQEEKYCVKGBD-UHFFFAOYSA-N InChI=1/C4H6/c1-3-4-2/h1-2H3Key: XNMQEEKYCVKGBD-UHFFFAOYAO SMILES C(#CC)C Chemical formula C4H6 Molar mass 54.0904 g/mol Density 0.691 g/mL Melting point −32 °C (−26 °F; 241 K) Boiling point 27 °C (81 °F; 300 K) Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is  ?) Infobox references

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 spectrum[3] leads to a determination that the torsional barrier is only 6 cm−1 (1.2×1022 J or 72 J mol−1). However, it has not been determined whether the equilibrium structure is eclipsed (D3h) or staggered (D3d). Symmetry analysis using the Molecular Symmetry Group[4] G36 shows that one would need to analyse its high resolution rotation-vibration Raman spectrum to determine its equilibrium structure.

2-Butyne (dimethylethin) forms with 5-decyne (dibutylethin), 4-octyne (dipropylethin) and 3-hexyne (diethylethin) a group of symmetric alkynes.

Synthesis

2-Butyne can be synthesized by the rearrangement of ethylacetylene in a solution of ethanolic potassium hydroxide.[5]

Applications

2-Butyne, along with propyne, is used to synthesize alkylated hydroquinones in the total synthesis of Vitamin E.[6]