Tricarbon monoxide

Tricarbon monoxide C3O is a reactive radical oxocarbon molecule found in space, and which can be made as a transient substance in the laboratory. It can be trapped in an inert gas matrix or made as a short lived gas. C3O can be classified as a ketene or an oxocumulene a kind of heterocumulene.[3]

Tricarbon monoxide
IUPAC name
Other names
3D model (JSmol)
Molar mass 52.032 g·mol−1
Appearance Gas
Related compounds
Related oxides
carbon monoxide
dicarbon monoxide
tetracarbon monoxide
Related compounds
tricarbon monosulfide
carbon subnitride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Natural occurrence

C3O has been detected by its microwave spectrum in the dark cold Taurus Molecular Cloud One[4] and also in the protostar Elias 18.[5]

The route to produce this is speculated to be:[6]

+ CO2 → HC3O+ + CO
HC3O+ → C3O + H+


C2 + CO → C3O which is more favourable at lower temperatures.

The related C3S is more abundant in dark molecular clouds, even though oxygen is 20 times more common than sulfur. The difference is due to the higher rate of formation and that C3S is less polar.[5]


C3O can be produced by heating Meldrum's acid. This also produces acetone, carbon monoxide and carbon dioxide.[7]

R. L. DeKock and W. Waltner were the first to identify C3O by reacting atomic carbon with carbon monoxide in an argon matrix. They observed an infrared absorption line at 2241 cm−1.[7] They produced carbon atoms by heating graphite inside a thin tantalum tube.[8]

M. E. Jacox photolysed C3O2 in an argon matrix to produce C3O with an IR absorption line at 2244 cm−1, however he did not recognise what was produced.[8]

By heating diazocyclopentanetrione or a similar acid anhydride, (2,4-azo-3-oxo-dipentanoic anhydride), C3O is produced. Also the action of light on tetracarbon dioxide yields C3O and CO.[9]

Heating fumaryl chloride also yields C3O.[3] Heating Lead 2,4-dinitroresorcinate also produces C3O along with C2O, CO and carbon suboxide.[10] An electric discharge in carbon suboxide produces about 11 ppm C3O.[11]

Roger Brown heated 3,5-dimethyl-1-propynolpyrazole to over 700 °C to make C3O.[12] Also pyrolysis of 5,5'-bis(2,2-dimethyl-4,6-dioxo-1,3-dioxanylidene or di-isopropylidene ethylenetetracarboxylate yields C3O.[12]

Irradiating carbon monoxide ice with electrons yields a mixture of carbon oxides, including C3O. This process could happen on icy bodies in space.[13]


C3O can be stabilised as a ligand in the pentacarbonyls of group 6 elements as in Cr(CO)5CCCO. This is formed from [n-Bu4N][CrI(CO)5] and the silver acetylide derivative of sodium propiolate (AgC≡CCOONa), and then thiophosgene. AgC≡CCOONa in turn is made from silver ions and sodium propiolate.[14] The blue black solid complex is called pentacarbony1(3-oxopropadienylidene)chromium(0). It is quite volatile and decomposes at 32 °C. Its infrared spectrum shows a band at 2028 cm−1 due to CCCO. The complex can dissolve in hexane, however it slowly decomposes, losing dicarbon (C2) which goes on to form acetylenes and cumulenes in the solvent. Dimethyl sulfoxide oxidises the CCCO ligand to carbon suboxide./[15]

C3O deposits a reddish-black film on glass.[12]

The reaction of C3O and urea is predicted to form uracil.[16] The pathway for this, is that firstly the two molecules react to form isocyanuric acid and propiolamide, the NH then reacts to bond with the triple bond, with the NH2 group moving back. Then a final cyclisation occurs to make uracil.[17]


The C3O molecules do not last long. At the low pressure of 1 pascal, they survive about one second.[18] The force constants for the bonds are:C1-O 14.94, C1-C2 1.39 C2-C3 6.02 mdyn/Å.[8] The bond lengths are C-O 1.149, C1-C2 1.300, C2-C3 1.273 Å. The molecule is linear.[6]

bond atom 1 atom 2 length
force constant
IR bands
CCC-O C1 O 1.149 14.94
CC-CO C2 C1 1.300 1.39
C-CCCO C3 C2 1.273 6.02

Proton affinity is 885 kJmol−1.[6] The dipole moment is 2.391 D.[14] The oxygen end has a positive charge, and the carbon end the negative charge.[6] The molecule behaves as if there are triple bonds at each end, and a single bond in the middle. This is isoelectronic to cyanogen.[19]

Molecular constants used in determining the microwave spectrum are rotational constant B0=4810.8862 MHz centrifugal distortion constant D0=0.00077 MHz. Known microwave spectral lines vary from 9621.76 for J=1←0 to 182792.35 MHz for J=19←18.[11]


  1. ^ Brown, Ronald D.; Rice, E. H. (October 1984). "Tricarbon monoxide - a theoretical study". Journal of the American Chemical Society. 106 (22): 6475–6478. doi:10.1021/ja00334a002.
  2. ^ Cooksy, A. L.; Watson, J. K. G.; Gottlieb, C. A.; Thaddeus, P. (February 1992). "The rotational spectrum of the carbon chain radical HCCCO". The Astrophysical Journal. 386: L27. Bibcode:1992ApJ...386L..27C. doi:10.1086/186284.
  3. ^ a b Ruppel, Raimund (1999). "Neue Heterokumulene und Carbene" (PDF) (in German). Gießen: Justus-Liebig-Universität: 13. Retrieved 10 November 2016. Cite journal requires |journal= (help)
  4. ^ Matthews, H. E.; Irvine, W. M.; Friberg, P; Brown, R. D.; Godfrey, P. D. (12 July 1984). "A new interstellar molecule: tricarbon monoxide". Nature. 310 (5973): 125–126. Bibcode:1984Natur.310..125M. doi:10.1038/310125a0. PMID 11541993.
  5. ^ a b c Abbas, Haider (6 February 2014). "Neutral-neutral reactions for the formation of C3O and C3S". Astrophysics and Space Science. 351 (1): 53–57. Bibcode:2014Ap&SS.351...53A. doi:10.1007/s10509-014-1809-y.
  6. ^ a b c d e Botschwina, Peter (1989). "A theoretical investigation of the astrophysically important molecules C3O and HC3O+". The Journal of Chemical Physics. 90 (8): 4301. Bibcode:1989JChPh..90.4301B. doi:10.1063/1.455787.
  7. ^ a b Brown, Ronald D.; Eastwood, Frank W.; Elmes, Patricia S.; Godfrey, Peter D. (October 1983). "Tricarbon monoxide". Journal of the American Chemical Society. 105 (21): 6496–6497. doi:10.1021/ja00359a026. image of the tricarbon monoxide research team
  8. ^ a b c d DeKock, R. L.; Weltner, W. (December 1971). "C2O, CN2, and C3O molecules". Journal of the American Chemical Society. 93 (25): 7106–7107. doi:10.1021/ja00754a081.
  9. ^ Maier, Günther; Reisenauer, Hans Peter; Balli, Heinz; Brandt, Willy; Janoschek, Rudolf (August 1990). "C4O2(1,2,3-Butatriene-1,4-dione), the First Dioxide of Carbon with an Even Number of C Atoms". Angewandte Chemie International Edition in English. 29 (8): 905–908. doi:10.1002/anie.199009051.
  10. ^ Tang T.B. (1 February 1985). "Tricarbon monoxide and dicarbon monoxide: Addendum to "decomposition of lead (ii) 2,4-dinitroresorcinate"". Thermochimica Acta. 83 (2): 397–398. doi:10.1016/0040-6031(85)87024-6.
  11. ^ a b Tang, Tong B.; Inokuchi, Hiroo; Saito, Shuji; Yamada, Chikashi; Hirota, Eizi (April 1985). "CCCO: Generation by dc glow discharge in carbon suboxide, and microwave spectrum". Chemical Physics Letters. 116 (1): 83–85. Bibcode:1985CPL...116...83T. doi:10.1016/0009-2614(85)80130-5.
  12. ^ a b c Brown, Roger F.C.; Godfrey, Peter D.; Lee, Swee Choo (1985). "Flash vacuum pyrolysis of 1-propynoylpyrazoles: a new precursor of tricarbon monoxide". Tetrahedron Letters. 26 (51): 6373–6376. doi:10.1016/S0040-4039(01)84602-5.
  13. ^ Jamieson, Corey S.; Mebel, Alexander M.; Kaiser, Ralf I. (March 2006). "Understanding the Kinetics and Dynamics of Radiation‐induced Reaction Pathways in Carbon Monoxide Ice at 10 K". The Astrophysical Journal Supplement Series. 163 (1): 184–206. Bibcode:2006ApJS..163..184J. CiteSeerX doi:10.1086/499245.
  14. ^ a b Baceiredo, Antoine (2010). Transition Metal Complexes of Neutral Eta1-Carbon Ligands. Springer Science & Business Media. pp. 247–248. ISBN 9783642047213.
  15. ^ Berke, Heinz; Härter, Peter (March 1980). "Complex Stabilization of 3-Oxopropadienylidene(C3O) with Pentacarbonylchromium(0)". Angewandte Chemie International Edition in English. 19 (3): 225–226. doi:10.1002/anie.198002251.
  16. ^ Wang, Tianfang; Bowie, John H. (November 2011). "Studies of cyclization reactions of linear cumulenes and heterocumulenes using the neutralization-reionization procedure and/or ab initio calculations". Mass Spectrometry Reviews. 30 (6): 1225–1241. Bibcode:2011MSRv...30.1225W. doi:10.1002/mas.20328.
  17. ^ Wang, Tianfang; Bowie, John H. (2012). "Can cytosine, thymine and uracil be formed in interstellar regions? A theoretical study". Org. Biomol. Chem. 10 (3): 652–662. doi:10.1039/C1OB06352A.
  18. ^ Information, Reed Business (9 May 1985). "Theory predicts a new oxide of carbon". New Scientist (1455): 21. Retrieved 10 November 2016.
  19. ^ Brown, Ronald D.; Pullin, David E.; Rice, Edward H. N.; Rodler, Martin (December 1985). "The infrared spectrum and force field of tricarbon monoxide". Journal of the American Chemical Society. 107 (26): 7877–7880. doi:10.1021/ja00312a013.
Aluminium(II) oxide

Aluminium(II) oxide or aluminium monoxide is a compound of aluminium and oxygen with the chemical formula AlO. It has been detected in the gas phase after explosion of aluminized grenades in the upper atmosphere and in stellar absorption spectra.


Benzonitrile is the chemical compound with the formula C6H5(CN), abbreviated PhCN. This aromatic organic compound is a colorless liquid with a sweet almond odour. It is mainly used as a precursor to the resin benzoguanamine.

Circumstellar envelope

A circumstellar envelope (CSE) is a part of a star that has a roughly spherical shape and is not gravitationally bound to the star core. Usually circumstellar envelopes are formed from the dense stellar wind, or they are present before the formation of the star. Circumstellar envelopes of old stars (Mira variables and OH/IR stars) eventually evolve into protoplanetary nebulae, and circumstellar envelopes of young stellar objects evolve into circumstellar discs.


Cyclopropenone is an organic compound with molecular formula C3H2O consisting of a cyclopropene carbon framework with a ketone functional group. It is a colorless, volatile liquid that boils near room temperature. Neat cyclopropenone polymerizes upon standing at room temperature. The chemical properties of the compound are dominated by the strong polarization of the carbonyl group, which gives a partial positive charge with aromatic stabilization on the ring and a partial negative charge on oxygen. It is an aromatic compound.

Dicarbon monoxide

Dicarbon monoxide (C2O) is a molecule that contains two carbon atoms and one oxygen atom. It is a linear molecule that, because of its simplicity, is of interest in a variety of areas. It is, however, so extremely reactive that it is not encountered in everyday life. It is classified as a cumulene and an oxocarbon.

Ethyl formate

Ethyl formate is an ester formed when ethanol (an alcohol) reacts with formic acid (a carboxylic acid). Ethyl formate has the characteristic smell of rum and is also partially responsible for the flavor of raspberries. It occurs naturally in the body of ants and in the stingers of bees.

Intergalactic dust

Intergalactic dust is cosmic dust in between galaxies in intergalactic space. Evidence for intergalactic dust has been suggested as early as 1949, and study of it grew throughout the late 20th century. There are large variations in the distribution of intergalactic dust. The dust may affect intergalactic distance measurements, such as to supernova and quasars in other galaxies.Intergalactic dust can form intergalactic dust clouds, known to exist around some galaxies since the 1960s. By the 1980s, at least four intergalactic dust clouds had been discovered within several megaparsec (Mpc) of the Milky Way galaxy, exemplified by the Okroy cloud.In February 2014, NASA announced a greatly upgraded database for tracking polycyclic aromatic hydrocarbons (PAHs) in the universe. According to scientists, more than 20% of the carbon in the universe may be associated with PAHs, possible starting materials for the formation of life. PAHs seem to have been formed as early as two billion years after the Big Bang, are widespread throughout the universe, and are associated with new stars and exoplanets.


Ketenimines are a group of organic compounds sharing a common functional group with the general structure R1R2C=C=NR3. A ketenimine is a cumulated alkene and imine and is related to an allene and a ketene.

The parent compound is ketenimine or CH2CNH. The most recent work by Bane et al. investigates the rovibrational structure of the ν8 and ν12 bands in the high-resolution FTIR spectrum, complementing the earlier analysis of the pure rotational spectrum. This pair of Coriolis coupled bands provide a rare example where intensity sharing between bands yields sufficient intensity for an otherwise invisible band (ν12).

Methoxy group

A methoxy group is the functional group consisting of a methyl group bound to oxygen. This alkoxy group has the formula O–CH3. On a benzene ring, the Hammett equation classifies a methoxy substituent as an electron-donating group.

Octatetraynyl radical

Octatetraynyl radical (C8H) is an organic free radical with eight carbon atoms linked in a chain with alternating single bonds and triple bonds.

In 2007 negatively charged octatetraynyl was detected in Galactic molecular source TMC-1, making it the second type of anion to be found in the interstellar medium (after Hexatriynyl radical) and the largest such molecule detected to date.

Phosphorus mononitride

Phosphorus mononitride is an inorganic compound with the chemical formula PN. Containing only phosphorus and nitrogen, this material is classified as a binary nitride.

It is the first identified phosphorus compound in the interstellar medium.It is an important molecule in interstellar medium and the atmospheres of Jupiter and Saturn.

Photodissociation region

Photodissociation regions (or photon-dominated regions, or PDRs) are predominantly neutral regions of the interstellar medium in which far ultraviolet photons strongly influence the gas chemistry and act as the most important source of heat. They occur in any region of interstellar gas that is dense and cold enough to remain neutral, but that has too low a column density to prevent the penetration of far-UV photons from distant, massive stars. A typical and well-studied example is the gas at the boundary of a giant molecular cloud. PDRs are also associated with HII regions, reflection nebulae, active galactic nuclei, and Planetary nebulae. All the atomic gas and most of the molecular gas in the galaxy is found in PDRs.


Propionaldehyde or propanal is the organic compound with the formula CH3CH2CHO. It is a saturated 3-carbon aldehyde and is a structural isomer of acetone. It is a colorless liquid with a slightly irritating, fruity odor.


Propynal is an organic compound with molecular formula HC2CHO. It is the simplest chemical compound containing both alkyne and aldehyde functional groups. It is a colorless liquid with explosive properties.The compound exhibits reactions expected for an electrophilic alkynyl aldehyde. It is a dienophile and a good Michael acceptor. Grignard reagents add to the carbonyl center.

Silicon monosulfide

Silicon monosulfide is a chemical compound of silicon and sulfur. The chemical formula is SiS. Molecular SiS has been detected at high temperature in the gas phase. The gas phase molecule has an Si-S bondlength of 192.93 pm, this compares to the normal single bond length of 216 pm, and is shorter than the Si=S bond length of around 201 pm reported in an organosilanethione. Historically a pale yellow-red amorphous solid compound has been reported. The behavior of silicon can be contrasted with germanium which forms a stable solid monosulfide.

Tetracarbon dioxide

Tetracarbon dioxide is an oxide of carbon, a chemical compound of carbon and oxygen, with chemical formula C4O2 or O=C=C=C=C=O. It can be regarded as butatriene dione, the double ketone of butatriene — more precisely 1,2,3-butatriene-1,4-dione.Butatriene dione is the fourth member of the family of linear carbon dioxides O(=C)n=O, that includes carbon dioxide CO2 or O=C=O, ethylene dione C2O2 or O=C=C=O, carbon suboxide C3O2 or O=C=C=C=O, pentacarbon dioxide C5O2 or O=C=C=C=C=C=O, and so on.

The compound was obtained in 1990 by Maier and others, by flash vacuum pyrolysis of cyclic azaketones in a frozen argon matrix. It was also obtained in the same year by Sülzle and Schwartz through impact ionization of ((CH3-)2(C4O2)(=O)2=)2 in the gas phase. Although theoretical studies indicated that the even-numbered members of the O(=C)n=O family should be inherently unstable, C4O2 is indefinitely stable in the matrix, but is decomposed by light into tricarbon monoxide C3O and carbon monoxide CO. It has a triplet ground state.

Titanium oxide

Titanium oxide may refer to:

Titanium dioxide (titanium(IV) oxide), TiO2

Titanium(II) oxide (titanium monoxide), TiO, a non-stoichiometric oxide

Titanium(III) oxide (dititanium trioxide), Ti2O3



δ-TiOx (x= 0.68–0.75)

TinO2n−1 where n ranges from 3–9 inclusive, e.g. Ti3O5, Ti4O7, etc.

Triatomic molecule

Triatomic molecules are molecules composed of three atoms, of either the same or different chemical elements. Examples include H2O, CO2 (pictured) and HCN.

Tricarbon monosulfide

Tricarbon monosulfide (C3S) or tricarbon sulfur is a reactive molecular substance found in space. Tricarbon monosulfide is a heterocumulene or thiocumulene, consisting of a straight chain of three carbon atoms and a terminal sulfur atom.

Common oxides
Exotic oxides
Compounds derived from oxides


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