Cyclo(18)carbon

The correct title of this article is Cyclo[18]carbon. The substitution of any brackets is due to technical restrictions.

Cyclooctadeca-1,3,5,7,9,11,13,15,17-nonayne or cyclo[18]carbon is an allotrope of carbon with molecular formula C
₁₈. The molecule is a ring of eighteen carbon atoms, connected by alternating triple and single bonds; thus, it is a polyyne and a cyclocarbon.

Cyclo[18]carbon

Names
Preferred IUPAC name Cyclooctadeca-1,3,5,7,9,11,13,15,17-nonayne
Identifiers
CAS Number	126487-09-0 Y
3D model (JSmol)	Interactive image
ChemSpider	74015635
PubChem CID	14940714
CompTox Dashboard (EPA)	DTXSID801267863
InChI InChI=1S/C18/c1-2-4-6-8-10-12-14-16-18-17-15-13-11-9-7-5-3-1 Key: GPWDPLKISXZVIE-UHFFFAOYSA-N
SMILES C1#CC#CC#CC#CC#CC#CC#CC#CC#C1
Properties
Chemical formula	C18
Molar mass	216.198 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Cyclo[18]carbon is the smallest cyclo[n]carbon predicted to be thermodynamically stable, with a computed strain energy of 72 kilocalories per mole.^[1] Above 122 K, it explosively decomposes to amorphous graphite.^[2]

A collaboration of teams at IBM and the University of Oxford team claimed to synthesize it in solid state in 2019^[3] by electrochemical decarbonylation of several sites of a cyclobutanone structure:^[4] Later, researchers from Spain have used computational techniques to probe the structural and electronic properties of the molecule, and have discovered it to be an electron acceptor.^[5]

Synthesis of cyclocarbon

According to these IBM researchers, the electronic structure of their product consists of alternating triple bonds and single bonds, rather than a cumulene-type structure of consecutive double bonds. This supposedly makes this molecule a semiconductor.^[4]

References

1. George A. Adamson; Charles W. Rees (1996). "Towards the total synthesis of cyclo[n]carbons and the generation of cyclo[6]carbon". J. Chem. Soc., Perkin Trans. 1 (13): 1535–1543. doi:10.1039/P19960001535.
2. 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.
3. Kaiser, Katharina; Scriven, Lorel M.; Schulz, Fabian; Gawel, Przemyslaw; Gross, Leo; Anderson, Harry L. (15 Aug 2019). "An sp-hybridized molecular carbon allotrope, cyclo[18]carbon". Science. 365 (6459): 1299–1301. arXiv:1908.05904. doi:10.1126/science.aay1914. PMID 31416933. S2CID 201019470.
4. Castelvecchi, Davide (15 August 2019). "Chemists make first-ever ring of pure carbon". Nature. 572 (7770): 426. doi:10.1038/d41586-019-02473-z. PMID 31431741.
5. Stasyuk, Anton J.; Stasyuk, Olga A.; Solà, Miquel; Voityuk, Alexander A. (29 Nov 2019). "Cyclo[18]carbon: the smallest all-carbon electron acceptor". Chemical Communications. 56 (3): 352–355. doi:10.1039/c9cc08399e. hdl:10256/17613. PMID 31825030. S2CID 209316603.