2-Butyne

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2-Butyne[1][2]
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Molar mass 54.0904 g/mol
Density 0.691 g/mL
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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.

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[3] leads to a determination that the torsional barrier is only 6 cm−1 (1.2Template:E 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][5] G36 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.[6]


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.[7]

Applications

2-Butyne, along with propyne, is used to synthesize alkylated hydroquinones in the total synthesis of Vitamin E.[8]

See also

References

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  1. [1] at Sigma-Aldrich
  2. NIST Chemistry WebBook page for 2-butyne
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