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

, 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; 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 covalently linked in 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 ...

. 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 (Tetravalence, tetravalent). Well-known forms of carbon include diamond and graphite. In recent ...

. Possible bonding patterns include all

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 (a 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 ...

) 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 Electron pair bond, bonding electrons instead of the usual two in a covalent bond, covalent single bond. Triple bonds are stronger than the equivalent covalent bond, sin ...

s (a cyclic

polyyne A polyyne is any organic compound with alternating Single bond, 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 products and ...

). The first cyclocarbon synthesized is cyclo 8arbon (C₁₈). Besides that, C₆, C₁₀, C₁₂, C₁₃, C₁₄, C₁₆, C₂₀, and C₂₆ are all known.

Cyclo arbon

The (

hypothetical A hypothesis (: hypotheses) is a proposed explanation for a phenomenon. A scientific hypothesis must be based on observations and make a testable and reproducible prediction about reality, in a process beginning with an educated guess or tho ...

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

Cyclo arbon

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

Cyclo 8arbon

The smallest cyclo 'n''arbon predicted to be relatively stable is C₁₈, with a computed

strain energy In physics, the elastic potential energy gained by a wire during elongation with a tensile (stretching) or compressive (contractile) force is called strain energy. For linearly elastic materials, strain energy is: : U = \frac 1 2 V \sigma \v ...

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 with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping level ...

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