Dicarbon monoxide () is a molecule that contains two carbon atoms and one oxygen atom. It is a linear molecule that, because of its simplicity, is of interest in a variety of areas. It is, however, so extremely reactive that it is not encountered in everyday life. It is classified as a carbene, cumulene and an oxocarbon.
Dicarbon monoxide is a product of the photolysis of carbon suboxide:
It is stable enough to observe reactions with NO and NO<sub>2</sub>.
Called ketenylidene in organometallic chemistry, it is a ligand observed in metal carbonyl clusters, e.g. [OC<sub>2</sub>Co<sub>3</sub>(CO)<sub>9</sub>]<sup>+</sup>. Ketenylidenes are proposed as intermediates in the chain growth mechanism of the Fischer-Tropsch Process, which converts carbon monoxide and hydrogen to hydrocarbon fuels.
The organophosphorus compound (C<sub>6</sub>H<sub>5</sub>)<sub>3</sub>PCCO (CAS# 15596-07-3) contains the C<sub>2</sub>O functionality. Sometimes called Bestmann's Ylide, it is a yellow solid.