1,3 Dioxetanedione

The chemical compound 1,3-dioxetanedione, or 1,3-dioxacyclobutane-2,4-dione is a hypothetical oxide of carbon with formula C₂O₄. It can be considered a cyclic dimer of carbon dioxide (CO₂) or as a double ketone of 1,3-dioxetane (1,3-dioxacyclobutane).

Theoretical calculations indicate that the compound is extremely unstable at room temperature (half-life of less than 1.1 μs); but may be stable at −196 °C.