Cyclocarbons

Cyclo[6]carbon is an allotrope of carbon with molecular formula . This theoretical molecule is a ring of six carbon atoms, connected by alternating double bonds. It is, therefore, a member of the [[cyclocarbon|cyclo[n]carbon]] family.

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

Cyclopropatriene is a hypothetical compound () which is an allotrope of carbon. It was once proposed as a candidate for a spectroscopically observed tricarbon species. It is a cyclic cumulene.

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).