Pentacarbon dioxide, officially penta-1,2,3,4-tetraene-1,5-dione, is an oxide of carbon (an oxocarbon) with formula C5O2 or O=C=C=C=C=C=O. The compound is the third member of the series CnO2 with odd n, the first two members being carbon dioxide (CO2) and carbon suboxide (C3O2). The compound was described in 1988 by G. Maier and others, who obtain...