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.

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 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 (D_3h) or staggered (D_3d). Symmetry analysis using the Molecular Symmetry Group 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.

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.

Applications

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

See also

• Acetylenedicarboxylic acid
• 1-Butyne, a position isomer
• 1,4-Butynediol
• Hexamethylbenzene, a product of 2-butyne trimerization
• Hexafluoro-2-butyne