|Molar mass||108.01 g/mol|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Carbon hexoxide or carbon hexaoxide is an oxide of carbon with an unusually large quantity of oxygen. The molecule has been produced and studied at cryogenic temperatures. The molecule is important in atmospheric chemistry and in the study of cold ices in the outer solar system and interstellar space. The substance could form and be present on Ganymede or Triton, moons in the outer solar system. The molecule consists of a six membered ring with five oxygen and one carbon atom, and one oxygen with a double bond with the carbon.
The molecule that has been observed has a Cs symmetry. The ring is not a flat hexagon but puckered with slightly different side lengths and angles (120°) from the regular hexagon. Going around the ring starting at the carbon to oxygen bond the interatomic distances are C-O: 1.362 Å O-O 1.491 Å O-O 1.391 Å O-O 1.391 Å O-O 1.491 Å O-C 1.362 Å. The angles between the bonds are: O-C-O 120.4 °C-O-O 115.7° O-O-O 105.9 ° and the opposite from carbon O-O-O 104.1°. For the double carbon to oxygen bond, the length is 1.185 Å and the angle from the single bonds is 119.6°.
In an experiment, carbon hexoxide was formed by irradiating solid carbon dioxide with electrons at an energy of 5000 V at 10K in a vacuum. The reaction proceeded by breaking atomic oxygen from the carbon dioxide. This then reacted with carbon dioxide to form O2CO. This further reacted to make the series of ring oxides: O3CO O4CO with the final one inserting an oxygen atom in the ring to form carbon hexoxide. The reaction O4CO + O → O5CO liberates 145.2 kJmol−1.
Other possible isomers of carbon hexoxide are the C2 form with a five and three membered ring, and the D2d with two four membered rings. The D2d O3CO3 isomer has a calculated C-O bond length of 1.391 Å, and an O-O length of 1.469 Å. The O-C-O bond angle is 94.1°. However these two isomers have not been observed.
- Jamieson, Corey S.; Alexander M. Mebel; Ralf I. Kaiser (2008). "First detection of the Cs symmetric isomer of carbon hexaoxide (CO6) at 10K". Chemical Physics Letters. 450 (4–6): 312–317. Bibcode:2008CPL...450..312J. ISSN 0009-2614. doi:10.1016/j.cplett.2007.11.052.
- Kaiser, Ralf I.; Alexander M. Mebel (2008). "On the formation of higher carbon oxides in extreme environments". Chemical Physics Letters. 465 (1–3): 1–9. Bibcode:2008CPL...465....1K. ISSN 0009-2614. doi:10.1016/j.cplett.2008.07.076.