Cyclocarbon

In organic chemistry, a cyclo[n]carbon (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 allotropes of carbon. Possible bonding patterns include all double bonds (a cyclic cumulene) or alternating single bonds and triple bonds (a cyclic polyyne).^[1]^[2]^[3]

As of 2020, the only cyclocarbon that has been synthesized is cyclo[18]carbon.

^ Cite error: The named reference adaree was invoked but never defined (see the help page).
^ Yves Rubin; Carolyn B. Knobler; Francois Diederich (1990). "Precursors to the cyclo[n]carbons: from 3,4-dialkynyl-3-cyclobutene-1,2-diones and 3,4-dialkynyl-3-cyclobutene-1,2-diols to cyclobutenodehydroannulenes and higher oxides of carbon". J. Am. Chem. Soc. 112 (4): 1607–1617. doi:10.1021/ja00160a047.
^ François Diederich; Yves Rubin; Carolyn B. Knobler; Robert L. Whetten; Kenneth E. Schriver; Kendall N. Houk; Yi Li (8 September 1989). "All-Carbon Molecules: Evidence for the Generation of Cyclo[18]carbon from a Stable Organic Precursor". Science. 245 (4922): 1088–1090. Bibcode:1989Sci...245.1088D. doi:10.1126/science.245.4922.1088. PMID 17838807. S2CID 23726682.