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Chemical structure of 1,4-pentadiyne
IUPAC name
3D model (
  • InChI=1S/C5H4/c1-3-5-4-2/h1-2H,5H2
  • C#CCC#C
Molar mass 64.087 g·mol−1
Appearance colorless liquid[1]
Melting point −21 – −19 °C (−6 – −2 °F; 252–254 K)[1]
Boiling point 61–64 °C (142–147 °F; 334–337 K)[2]
1.4283 (23 °C)[2]
0.516 D
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

1,4-Pentadiyne (penta-1,4-diyne) is a chemical compound belonging to the alkynes. The compound is the structural isomer to 1,3-pentadiyne.


Until the late 1960s, no successful synthesis of this seemingly simply preparable molecule was described. Although long-chain and more complex 1,4-diynes had been synthesized successfully before,

sodium acetylide and propargyl bromide or from the acetylene Grignard reagent with propargyl bromide and copper(I) chloride failed[5] and mostly 1,3-pentadiyne was obtained as rearrangement product.[1]

The successful isolation in small amounts succeeded by reacting propargyl bromide and to the respective

GLC of the distillate.[1][2]

An improved synthesis method was published by Verkruijsse and Hasselaar in 1979. Copper chloride was substituted by copper(I) bromide as well as propargyl bromide by propargyl tosylate. At lower reaction temperatures and fewer by-products, the alkiyne was obtained after multistep extraction. According to the publication’s authors, this circumvented the problem that the solvent THF and the main compound share similar boiling points.[2]

Preparation of 1,4-pentadiyne by Verkruijsse and Hasselaar

Moreover, a

UV radiation is possible.[7]

1,4-Pentadiyne forms at the pyrolisis or photoinduced decomposition of 3-ethynylcycloprop-1-ene

The compounds forms also during the exothermic reaction of

allene and the ethynyl radical. This reaction is mainly of interest for astrochemistry.[8][9][10]


At room temperature the substance discolors from a colorless to a yellowish liquid, however, storage in diluted solutions at 0 °C is possible for multiple weeks.[1]

While for 1,4-pentadiene the sp2-

p orbital lobes close to the sp3-hybridized carbon has been postulated.[11] According to a QCSID(T) calculation, the alkiyne is destabilized relative to 1,3-pentadiyne by 25 kcal · mol−1.[12]

Although microwave spectroscopy revealed besides a dipole moment of 0.516 D no significant distortions compared to an ideal tetrahedron, three different ionization energies are reported for the π-system.[3]


1,4-pentadiyne is a common starting material for the synthesis of

phosphabenzene and their substituted derivates.[13][14]

1,4-Pentadiin is used in the preparation of heterobenzenes