What is "pentacarbon dioxide"

n. (context organic compound English) The linear oxocarbon having five carbon atoms

Pentacarbon dioxide, officially penta-1,2,3,4-tetraene-1,5-dione, is an oxide of carbon (an oxocarbon) with formula CO or O=C=C=C=C=C=O.

The compound is the third member of the series CO with odd n, the first two members being carbon dioxide (CO) and carbon suboxide (CO). The compound was described in 1988 by G. Maier and others, who obtained it by pyrolysis of 1,3,5-cyclohexanetrione (phloroglucin, the tautomeric form of phloroglucinol). It has also been obtained by flash vapor pyrolysis of 2,4,6-tris(diazo)cyclohexane-1,3,5-trione (CNO). It is stable at room temperature in solution. The pure compound is stable up to −96 °C, when it polymerizes.