Cyclopropanetrione

Cyclopropanetrione or trioxocyclopropane is a little-known oxide of carbon with formula C₃O₃. It consists of a ring of three carbon atoms each attached to an oxygen atom with a double bond. Alternately it can be thought as a trimer of carbon monoxide. This compound is thermodynamically unstable, and has not been produced in bulk. However it has been detected using mass spectrometry.

It is the neutral equivalent of the deltate anion C₃O₃²⁻, known since 1975. An equivalent hydrate hexahydroxycyclopropane or cyclopropane-1,1,2,2,3,3-hexol, (-C(OH)₂-)₃ also exists. This contains geminal hydroxy groups.