Article · Wikipedia archive · Last revised Jul 30, 2026

Propadienone

Propadienone is an organic compound with the molecular formula H2C=C=C=O. It is the parent compound of the alkylidene ketenes, and the first member of the homologous series of cumulenones H2C=(C=)nC=O.

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Jul 30, 2026
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Propadienone
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Names
IUPAC name
1,2-Propadien-1-one
Other names
  • 1-Allenone
  • Methylene ketene
Identifiers
3D model (JSmol)
ChemSpider
  • InChI=1S/C3H2O/c1-2-3-4/h1H2
    Key: TURAMGVWNUTQKH-UHFFFAOYSA-N
  • C=C=C=O
Properties
C3H2O
Molar mass 54.048 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Propadienone is an organic compound with the molecular formula H2C=C=C=O. It is the parent compound of the alkylidene ketenes,1 and the first member of the homologous series of cumulenones H2C=(C=)nC=O.2

Synthesis

Propadienone may be generated via flash vacuum pyrolysis of several possible precursors, including acrylic anhydride and 3-diazotetronic acid.3 While it is only transiently present under standard conditions, it may be captured via matrix isolation in solid argon at 14 K.3

Structure

While the ground state of propadienone is planar, it has a nonlinear CCCO backbone, in contrast to cumulenes, as well as heterocumulenes such as carbon suboxide.45 The barrier to backbone linearization is at least 360 cm−1, much larger than the higher cumulenones H2C=(C=)2C=O and H2C=(C=)3C=O, which are predicted to also be bent but with very small barriers to linearization (<30 cm−1).2

Its C1 bond angle (C–C–O) is 166–173° and its C2 bond angle (C–C–C) is 142–144°, bending in opposite directions to each other in a zigzag geometry.26 The large deviation of the C2 bond angle from linearity is attributable to H2C=C−−C≡O+ being a major resonance contributor, making propadienone a 1,3-dipole, a property that is shared by the higher cumulenones.26 Its dipole moment is 2.3 D.2

Propadienone is isoelectronic to diazoethene (H2C=C=N+=N−), which is predicted to also be bent.7

Reactions

Exposure of matrix-isolated propadienone to UV light of wavelength 230 ± 10 nm leads to its photodissociation into acetylene and carbon monoxide via a postulated methylidenecarbene intermediate.3 The same decarbonylation reaction occurs during vacuum pyrolysis at temperatures at or above 570 °C.8

Warming matrix-isolated propadienone yields a white insoluble polymer of unknown composition. The same polymer is also obtainable from direct low-temperature condensation of the undiluted pyrolysis gas stream.3

References

References

  1. Lorenčak, Primoz; Pommelet, J. C.; Chuche, Josselin; Wentrup, Curt [at Wikidata] (1986). "A stable methyleneketene and the stepwise fragmentation of Meldrum's acids". Chemical Communications (5): 369–370. doi:10.1039/C39860000369.
  2. Scott, Anthony P.; Radom, Leo (December 2000). "Are cumulenones kinked? A systematic high-level ab initio study of H2CCCO, H2CCCCO and H2CCCCCO". Journal of Molecular Structure. 556 (1–3): 253–261. Bibcode:2000JMoSt.556..253S. doi:10.1016/S0022-2860(00)00640-2.
  3. Chapman, Orville L. [in German]; Miller, Michael D.; Pitzenberger, Steven M. (October 1987). "Infrared spectroscopy of matrix-isolated propadienone". Journal of the American Chemical Society. 109 (22): 6867–6868. Bibcode:1987JAChS.109.6867C. doi:10.1021/ja00256a060.
  4. Brown, Ronald D.; Godfrey, Peter D.; Champion, Robert; McNaughton, Donald (September 1981). "Microwave spectrum and unusual geometry of propadienone (methylene ketene)". Journal of the American Chemical Society. 103 (19): 5711–5715. Bibcode:1981JAChS.103.5711B. doi:10.1021/ja00409a016.
  5. Brown, Ronald D.; Godfrey, Peter D.; Champion, Robert; McNaughton, Donald (November 1982). "Additions and Corrections - Microwave Spectrum and Unusual Geometry of Propadienone (Methylene Ketene)". Journal of the American Chemical Society. 104 (22): 6167. Bibcode:1982JAChS.104.6167B. doi:10.1021/ja00386a604.
  6. Brown, Ronald D.; Champion, Robert; Elmes, Patricia S.; Godfrey, Peter D. (July 1985). "The structure of propadienone". Journal of the American Chemical Society. 107 (14): 4109–4112. Bibcode:1985JAChS.107.4109B. doi:10.1021/ja00300a001.
  7. Murcko, Mark A.; Pollack, Steven K.; Lahti, Paul M. (January 1988). "An ab initio study of diazoethene, a propadienone isoelectronic with a bent structure". Journal of the American Chemical Society. 110 (2): 364–368. Bibcode:1988JAChS.110..364M. doi:10.1021/ja00210a007.
  8. Brown, Roger F. C.; Eastwood, Frank W.; McMullen, Gabrielle L. (October 1976). "Evidence for the pyrolytic generation of methyleneketene (propadienone)". Journal of the American Chemical Society. 98 (23): 7421–7422. Bibcode:1976JAChS..98.7421B. doi:10.1021/ja00439a052.