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 relatively stable, with a computed strain energy of 72 kilocalories per mole.^[1][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]