Propadienone
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| Names | |
|---|---|
| IUPAC name
1,2-Propadien-1-one | |
Other names
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| Identifiers | |
3D model (JSmol) |
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| ChemSpider | |
PubChem CID |
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CompTox Dashboard (EPA) |
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| 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).
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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
[edit]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
[edit]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.[4][5] 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.[2][6] 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.[2][6] 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
[edit]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
[edit]- ↑ 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.
- 1 2 3 4 5 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.
- 1 2 3 4 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.
- ↑ 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.
- ↑ 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.
- 1 2 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.
- ↑ 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.
- ↑ 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.