organic chemistry Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J.; ...

, a cyclo 'n''arbon (or simply cyclocarbon) is a

chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...

consisting solely of a number ''n'' of

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

atoms covalently linked in a

ring Ring 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 :(hence) to initiate a telephone connection Arts, entertainment and media Film and ...

. Since the compounds are composed only of carbon atoms, they are

allotropes of carbon Carbon is capable of forming many allotropy, allotropes (structurally different forms of the same element) due to its Valence (chemistry), valency. Well-known forms of carbon include diamond and graphite. In recent decades, many more allotrope ...

. Possible bonding patterns include all double bonds (a cyclic cumulene) or alternating

single bond In chemistry, a single bond is a chemical bond between two atoms involving two valence electrons. That is, the atoms share one pair of electrons where the bond forms. Therefore, a single bond is a type of covalent bond. When shared, each of th ...

s and

triple bond A triple bond in chemistry is a chemical bond between two atoms involving six bonding electrons instead of the usual two in a covalent single bond. Triple bonds are stronger than the equivalent single bonds or double bonds, with a bond order o ...

s (a cyclic

polyyne In organic chemistry, a polyyne () is any organic compound with alternating single and triple bonds; that is, a series of consecutive alkynes, with ''n'' greater than 1. These compounds are also called polyacetylenes, especially in the natural p ...

). As of 2020, the only cyclocarbon that has been synthesized is cyclo 8arbon.

Cyclo arbon

The (

hypothetical A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous obser ...

) three-carbon member of this family () is also called

cyclopropatriene Cyclopropatriene is a hypothetical compound () which is an allotrope of carbon. It was once proposed as a candidate for a spectroscopically observed tricarbon species. It is a cyclic cumulene In organic chemistry, a cumulene is a compound hav ...

Cyclo arbon

The (hypothetical) six-carbon member of this family () is also called

benzotriyne Benzotriyne or cyclo arbon is a hypothetical compound, an allotrope of carbon with molecular formula . The molecule is a ring of six carbon atoms, connected by alternating triple and single bonds. It is, therefore, a potential member of the c ...

Cyclo 8arbon

The smallest cyclo 'n''arbon predicted to be

thermodynamically stable In chemistry, chemical stability is the thermodynamic stability of a chemical system. Thermodynamic stability occurs when a system is in its lowest energy state, or in chemical equilibrium with its environment. This may be a dynamic equilibriu ...

is C₁₈, with a computed strain energy of 72 kilocalories per mole. An IBM/Oxford team claimed to synthesize its molecules in solid state in 2019: Synthesis of cyclocarbon

According to these IBM researchers, the synthesized cyclocarbon has alternating triple and single bonds, rather than being made of entirely of double bonds. This supposedly makes this molecule a

semiconductor A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...

Large cyclo arbons

Seenithurai & Chai 2020 found that larger cyclo arbons p to 100 carbon atomsexhibit polyradical character and report linear carbon chains (l-CC as well as cyclic carbon chain or cyclo carbon (c-CC , where n=10-100. For all the cases investigated, ''l''-CC 'n''and ''c''-CC 'n''are ground-state singlets, and ''c''-CC 'n''are energetically more stable than ''l''-CC 'n'' The electronic properties of ''l''-CC 'n''and ''c''-CC 'n''display peculiar oscillation patterns for smaller values of ''n'', followed by monotonic changes for larger values of ''n''. For the smaller carbon chains, odd-numbered ''l''-CC 'n''are more stable than the adjacent even-numbered ones, and ''c''-CC ''m+2''''c''-CC ''m''(where ''m'' are positive integers) are more/less stable than the adjacent odd-numbered ones. With the increase of ''n'', ''l''-CC 'n''and ''c''-CC 'n''possess increasing polyradical nature in their ground states, with the active orbitals being delocalized over the entire length of ''l''-CC 'n''or the whole circumference of ''c''-CC 'n'' On the basis of TAO-LDA results, the smaller ''c''-CC (up to = 22, where ''m'' are positive integers) possess nonradical nature and sizable singlet-triplet energy gaps (e.g., larger than 20 kcal/mol). In view of their high stability, it can be anticipated that these relatively stable cyclic carbon chains, such as ''c''-CC 0 ''c''-CC 4 ''c''-CC 8 and ''c''-CC 2 are likely to be synthesized in the near future. Among them, ''c''-CC 8(i.e. cyclo 8arbon) has been recently synthesized by an IBM/Oxford team in 2019.

References

{{Allotropes of carbon Allotropes of carbon