Carbon hexoxide

Carbon hexoxide or carbon hexaoxide is an oxide of carbon with an unusually large quantity of oxygen.[1] 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.[2] 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.[1]

Carbon hexoxide
carbon hexoxide model
3D model (JSmol)
Molar mass 108.01 g/mol
Related compounds
Related compounds
Carbon pentoxide
Carbon tetroxide
Carbon hexasulfide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).


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, and 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°.[1]


In an experiment, carbon hexoxide was formed by irradiating solid carbon dioxide with electrons at an energy of 5000 V at 10 K in a vacuum. The reaction proceeds by breaking atomic oxygen from carbon dioxide:

CO2 CO + O

The atomic oxygen then reacts with carbon dioxide to form carbon trioxide, and similar reactions occur to generate the series of ring oxides carbon tetroxide and carbon pentoxide, ultimately leading to the formation of carbon hexoxide[1] in an exothermic reaction.[2]

CO2 + O O2CO
O4CO + O O5CO ΔH = −145.2 kJ mol−1[2]


Carbon hexoxide is stable up to 60 K.[1] Vibrational infrared wavenumbers include the most prominent ν1 = 1876 cm−1 for the most common isotopologue 12C16O6.[1]

Other isomers

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.[2]

The equivalent carbon hexasulfide is also known from inert gas matrix study. It has C2 symmetry with the same atomic arrangement as the hexoxide.[3]


  1. ^ a b c d e f Jamieson, Corey S.; Alexander M. Mebel; Ralf I. Kaiser (2008). "First detection of the Cs symmetric isomer of carbon hexaoxide (CO6) at 10 K". Chemical Physics Letters. 450 (4–6): 312–317. Bibcode:2008CPL...450..312J. doi:10.1016/j.cplett.2007.11.052. ISSN 0009-2614.
  2. ^ a b c d 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. doi:10.1016/j.cplett.2008.07.076. ISSN 0009-2614.
  3. ^ Maity, Surajit; Kim, Y.S.; Kaiser, Ralf I.; Lin, Hong Mao; Sun, Bian Jian; Chang, A.H.H. (July 2013). "On the detection of higher order carbon sulfides (CSx; x = 4–6) in low temperature carbon disulfide ices". Chemical Physics Letters. 577: 42–47. Bibcode:2013CPL...577...42M. doi:10.1016/j.cplett.2013.05.039.
Carbon pentoxide

Carbon pentaoxide or carbon pentoxide is an unstable molecular oxide of carbon. 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 has a C2 symmetry. It consists of a five membered ring with one carbon and four oxygen atoms. A fifth oxygen atom has a double bond to the carbon. Calculation has resulted in a theoretical structure. The pentagon is not regular, but varies in the length of its sides and angles. The distance between the oxygen atoms that are not attached to carbon is 1.406 Å, whereas the distance between one of these atoms and an oxygen attached to carbon is 1.457 Å. The carbon oxygen bond length is 1.376 Å. The double carbon to oxygen bond is the shortest at 1.180 Å. There is no carbon-to-carbon bond as there is only one carbon atom. The OOO bond angle is 100.2° and the OOC angle is 109.1°. The OCO bond angle is 125.4°.


An oxocarbon or oxide of carbon is a chemical compound consisting only of carbon and oxygen.The simplest and most common oxocarbons are carbon monoxide (CO) and carbon dioxide (CO2) with IUPAC names carbon(II) oxide and carbon(IV) oxide respectively. Many other stable (practically if not thermodynamically) or metastable oxides of carbon are known, but they are rarely encountered, such as carbon suboxide (C3O2 or O=C=C=C=O) and mellitic anhydride (C12O9).

While textbooks will often list only the first three, and rarely the fourth, a large number of other oxides are known today, most of them synthesized since the 1960s. Some of these new oxides are stable at room temperature. Some are metastable or stable only at very low temperatures, but decompose to simpler oxocarbons when warmed. Many are inherently unstable and can be observed only momentarily as intermediates in chemical reactions or are so reactive that they can exist only in the gas phase or under matrix isolation conditions.

The inventory of oxocarbons appears to be steadily growing. The existence of graphene oxide and of other stable polymeric carbon oxides with unbounded molecular structures suggests that many more remain to be discovered.

Common oxides
Exotic oxides
Compounds derived from oxides


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