Cyclopentanepentone, also known as leuconic acid, is a hypothetical organic compound with formula C5O5, the fivefold ketone of cyclopentane. It would be an oxide of carbon (an oxocarbon), indeed a pentamer of carbon monoxide.

As of 2000, the compound had yet to be synthesized in bulk, but there have been reports of trace synthesis.[2][3][4]

Skeletal formula of cyclopentanepentone
leuconic acid molecule
Systematic IUPAC name
Other names
Leuconic acid
3D model (JSmol)
Molar mass 140.050 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Related compounds

Cyclopentanepentone can be viewed as the neutral counterpart of the croconate anion C

The compound referred to in the literature and trade as "cyclopentanepentone pentahydrate" (C5O5·5H2O) is probably decahydroxycyclopentane (C5(OH)10).[3][5]


  1. ^ "CID 12305030 - PubChem Public Chemical Database". The PubChem Project. USA: National Center for Biotechnology Information.
  2. ^ Rubin, M. B.; Gleiter, R. (2000). "The Chemistry of Vicinal Polycarbonyl Compounds". Chemical Reviews. 100 (3): 1121–64. doi:10.1021/cr960079j. PMID 11749259.
  3. ^ a b Seitz, G.; Imming, P. (1992). "Oxocarbons and pseudooxocarbons". Chemical Reviews. 92 (6): 1227–1260. doi:10.1021/cr00014a004.
  4. ^ Schröder, D.; Schwarz, H.; Dua, S.; Blanksby, S. J.; Bowie, J. H. (1999). "Mass spectrometric studies of the oxocarbons CnOn (n = 3–6)". International Journal of Mass Spectrometry. 188 (1–2): 17–25. doi:10.1016/S1387-3806(98)14208-2.
  5. ^ Person, W. B.; Williams, D. G. (1957). "Infrared Spectra and the Structure of Leuconic Acid and Triquinoyl". Journal of Physical Chemistry. 61 (7): 1017–1018. doi:10.1021/j150553a047.

See also


1,2,3,4,5-Cyclopentanepentol, also named cyclopentane-1,2,3,4,5-pentol or 1,2,3,4,5-pentahydroxycyclopentane is a chemical compound with formula C5H10O5 or (–CHOH–)5, whose molecule consists of a ring of five carbon atoms (a cyclopentane skeleton), each connected to one hydrogen and one hydroxyl group. The unqualified term "cyclopentanepentol" usually refers to this compound. There are four distinct stereoisomers with this same structure.The compound is a five-fold alcohol of cyclopentane, and technically a cyclic sugar alcohol (a cyclitol). However it is very rarely found in nature, and therefore it has received much less attention than the ubiquitous six-carbon version, inositol.


Carbon (from Latin: carbo "coal") is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Three isotopes occur naturally, 12C and 13C being stable, while 14C is a radionuclide, decaying with a half-life of about 5,730 years. Carbon is one of the few elements known since antiquity.Carbon is the 15th most abundant element in the Earth's crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. Carbon's abundance, its unique diversity of organic compounds, and its unusual ability to form polymers at the temperatures commonly encountered on Earth enables this element to serve as a common element of all known life. It is the second most abundant element in the human body by mass (about 18.5%) after oxygen.The atoms of carbon can bond together in different ways, termed allotropes of carbon. The best known are graphite, diamond, and amorphous carbon. The physical properties of carbon vary widely with the allotropic form. For example, graphite is opaque and black while diamond is highly transparent. Graphite is soft enough to form a streak on paper (hence its name, from the Greek verb "γράφειν" which means "to write"), while diamond is the hardest naturally occurring material known. Graphite is a good electrical conductor while diamond has a low electrical conductivity. Under normal conditions, diamond, carbon nanotubes, and graphene have the highest thermal conductivities of all known materials. All carbon allotropes are solids under normal conditions, with graphite being the most thermodynamically stable form at standard temperature and pressure. They are chemically resistant and require high temperature to react even with oxygen.

The most common oxidation state of carbon in inorganic compounds is +4, while +2 is found in carbon monoxide and transition metal carbonyl complexes. The largest sources of inorganic carbon are limestones, dolomites and carbon dioxide, but significant quantities occur in organic deposits of coal, peat, oil, and methane clathrates. Carbon forms a vast number of compounds, more than any other element, with almost ten million compounds described to date, and yet that number is but a fraction of the number of theoretically possible compounds under standard conditions. For this reason, carbon has often been referred to as the "king of the elements".

Carbon monoxide

Carbon monoxide (CO) is a colorless, odorless, and tasteless flammable gas that is slightly less dense than air. It is toxic to animals that use hemoglobin as an oxygen carrier (both invertebrate and vertebrate) when encountered in concentrations above about 35 ppm, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal biological functions. In the atmosphere, it is spatially variable and short lived, having a role in the formation of ground-level ozone.

Carbon monoxide consists of one carbon atom and one oxygen atom, connected by a triple bond that consists of two covalent bonds as well as one dative covalent bond. It is the simplest oxocarbon and is isoelectronic with other triply-bonded diatomic molecules having ten valence electrons, including the cyanide anion, the nitrosonium cation and molecular nitrogen. In coordination complexes the carbon monoxide ligand is called carbonyl.

Croconic acid

Croconic acid or 4,5-dihydroxycyclopentenetrione is a chemical compound with formula C5H2O5 or (C=O)3(COH)2. It has a cyclopentene backbone with two hydroxyl groups adjacent to the double bond and three ketone groups on the remaining carbon atoms. It is sensitive to light, soluble in water and ethanol and forms yellow crystals that decompose at 212 °C.The compound is acidic and loses the protons from the hydroxyl groups (pKa1 = 0.80±0.08 and pKa2 = 2.24±0.01 at 25 °C). The resulting anions, hydrogencroconate C5HO−5 and croconate C5O2−5 are also quite stable. The croconate ion, in particular, is aromatic and symmetric, as the double bond and the negative charges become delocalized over the five CO units (with six electrons, Hückel's rule means this is an aromatic configuration). The lithium, sodium and potassium croconates crystallize from water as dihydrates but the orange potassium salt can be dehydrated to form a monohydrate. The croconates of ammonium, rubidium and caesium crystallize in the anhydrous form. Salts of barium, lead, silver, and others are also known.Croconic acid also forms ethers such as dimethyl croconate where the hydrogen atom of the hydroxyl group is substituted with an alkyl group.


Cyclobutanetetrone, also called tetraoxocyclobutane, is an organic compound with formula C4O4 or (CO)4, the fourfold ketone of cyclobutane. It would be an oxide of carbon, indeed a tetramer of carbon monoxide.

The compound seems to be thermodynamically unstable. As of 2000, it had yet to be synthesized in significant amounts but may have transient existence as detected by mass spectrometry.


Cyclohexanehexone, also known as hexaketocyclohexane and triquinoyl, is an organic compound with formula C6O6, the sixfold ketone of cyclohexane. It is an oxide of carbon (an oxocarbon), a hexamer of carbon monoxide.

The compound is expected to be highly unstable, unlike the cyclohexanehexathione analog, and as of 1999 had only been observed as an ionized fragment during mass spectrometry studies.


Decahydroxycyclopentane is an organic compound with formula C5O10H10 or C5(OH)10. It is a fivefold geminal diol on a cyclopentane backbone.

The compound can be regarded as the fivefold hydrate of cyclopentanepentone. Indeed, the product referred to in the literature and trade as "cyclopentanepentone pentahydrate" (C5O5·5H2O) is now believed to be the decahydroxycyclopentane.The compound was synthetized by Heinrich Will in 1861, although for a long time it was believed to be a hydrate of C5O5. It can be prepared by oxidation of croconic acid C5O3(OH)2 with nitric acid. It can be isolated as water-soluble colorless crystals that melt with dehydration at about 115 °C, and slowly decompose at about 160 °C.

Oxocarbon anion

In chemistry, an oxocarbon anion is a negative ion consisting solely of carbon and oxygen atoms, and therefore having the general formula CxOn−y for some integers x, y, and n.

The most common oxocarbon anions are carbonate, CO2−3, and oxalate, C2O2−4. There is however a large number of stable anions in this class, including several ones that have research or industrial use. There are also many unstable anions, like CO−2 and CO−4, that have a fleeting existence during some chemical reactions; and many hypothetical species, like CO4−4, that have been the subject of theoretical studies but have yet to be observed.

Stable oxocarbon anions form salts with a large variety of cations. Unstable anions may persist in very rarefied gaseous state, such as in interstellar clouds. Most oxocarbon anions have corresponding moieties in organic chemistry, whose compounds are usually esters. Thus, for example, the oxalate moiety [–O–(C=O)2–O–] occurs in the ester dimethyl oxalate H3C–O–(C=O)2–O–CH3.

Common oxides
Exotic oxides
Compounds derived from oxides


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