Cyclo arbon is an allotrope of carbon with

molecular formula A chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as paren ...

. This theoretical molecule is a

ring (The) Ring(s) may refer to: * Ring (jewellery), a round band, usually made of metal, worn as ornamental jewelry * To make a sound with a bell, and the sound made by a bell Arts, entertainment, and media Film and TV * ''The Ring'' (franchise), a ...

of six

carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

atoms, connected by alternating

double bond In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betw ...

s. It is, therefore, a member of the cyclo 'n''arbon family. There have been a few attempts to synthesize cyclo arbon, e.g. by

pyrolysis Pyrolysis is a process involving the Bond cleavage, separation of covalent bonds in organic matter by thermal decomposition within an Chemically inert, inert environment without oxygen. Etymology The word ''pyrolysis'' is coined from the Gree ...

mellitic anhydride Mellitic anhydride, the anhydride of mellitic acid, is an organic compound with the formula C12O9. Containing no other elements (e.g., hydrogen) besides carbon and oxygen, mellitic anhydride is an oxide of carbon (oxocarbon), and, along with CO ...

, but without success until 2023, when it was successfully synthesised by atom manipulation of

hexachlorobenzene Hexachlorobenzene, or perchlorobenzene, is an aryl chloride and a six-substituted chlorobenzene with the molecular formula C6Cl6. It is a fungicide formerly used as a seed treatment, especially on wheat to control the fungal disease bunt. Its u ...

, although more thorough research has yet to be reported in peer reviewed scientific work. Another synthesis was reported in 2025 by the dehalogenation of hexaiodobenzene on a

sodium chloride Sodium chloride , commonly known as Salt#Edible salt, edible salt, is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. It is transparent or translucent, brittle, hygroscopic, and occurs a ...

layer on an Au(111) surface. The molecule's structure presents double bonds in sequence in a bent fashion, which is not explained by

valence bond theory In chemistry, valence bond (VB) theory is one of the two basic theories, along with molecular orbital (MO) theory, that were developed to use the methods of quantum mechanics to explain chemical bonding. It focuses on how the atomic orbitals of ...

for organic molecules, that describes double bonds by combinations of hybridised sp² orbitals, limiting the molecule's geometry in terms of increase of energy due to bond angles. Cyclo arbon would present then low probability of formation due to its high energy state from a thermodynamical perspective, which is reflected on the lack of evidence of its successful synthesis. Calculations suggest that the alternative cyclic

cumulene A cumulene is a compound having three or more ''cumulative'' (consecutive) double bonds. They are analogous to allenes, only having a more extensive chain. The simplest molecule in this class is butatriene (), which is also called simply ''cumu ...

structure, called cyclohexahexaene, is the potential energy minimum of the cyclo arbon framework.

References

{{Allotropes of carbon Cyclocarbons Polyynes Six-membered rings Cycloalkynes