Editing Ketene (section)

==Properties==
Ketenes are highly electrophilic at the carbon atom bonded with the heteroatom, due to its ''sp'' character. Ketenes can be formed with different heteroatoms bonded to the ''sp'' carbon atom, such as [[oxygen|O]], [[sulphur|S]] or [[selenium|Se]], respectively called ketenes, [[thioketene|thioketenes]] and selenoketenes.

[[Ethenone]], the simplest ketene, has different experimental lengths for each of its double bonds; the C=O bond is 1.160 [[Angstrom|Å]] and the C=C bond is 1.314 Å. The angle between the two [[Hydrogen|H]] atoms is 121.5°, similar to the theoretically ideal angle in [[alkene]]s between ''sp<sup>2</sup> ''carbon atoms and H substituents.<ref>{{Cite journal | first1 = Ngai Ling | last1 = Ma |first2 = MingWah | last2 = Wong | name-list-style = vanc |year=2000 |title=A Theoretical Study of the Properties and Reactivities of Ketene, Thioketene, and Selenoketene|url=https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/(SICI)1099-0690(200004)2000:8%3C1411::AID-EJOC1411%3E3.0.CO;2-N |journal=European Journal of Organic Chemistry |volume=2000 |issue=8 |pages=1411_1421 |doi=10.1002/(SICI)1099-0690(200004)2000:8<1411::AID-EJOC1411>3.0.CO;2-N}}</ref>

Ketenes are unstable and cannot be stored. In the absence of nucleophiles with which to react, ethenone dimerises to give β-[[lactone]], a cyclic [[ester]]. If the ketene is disubstituted, the dimerisation product is a substituted cyclobutadione. For monosubstituted ketenes, the dimerisation could afford either the ester or the diketone product.