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In organic chemistry, a cyclo 'n''arbon (or simply cyclocarbon) is a chemical compound consisting solely of a number ''n'' of carbon atoms covalently linked in a ring. Since the compounds are composed only of carbon atoms, they are
The ( hypothetical) three-carbon member of this family () is also called cyclopropatriene.
The (hypothetical) six-carbon member of this family () is also called benzotriyne.
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.
Seenithurai & Chai 2020 found that larger cyclo arbons
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 bonds (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 8arbon
The smallest cyclo 'n''arbon predicted to be thermodynamically stable 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:
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.
p to 100 carbon atoms
P, or p, is the sixteenth letter of the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''pee'' (pronounced ), plural ''pees''.
History
Th ...
exhibit 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