C6H4.C2O2.C6H4

from The Collaborative International Dictionary of English v.0.48

Anthraquinone \An`thra*qui"none\, n. [Anthracene + quinone.]
   (Chem.)
   A hydrocarbon, {C6H4.C2O2.C6H4}, subliming in shining yellow
   needles. It is obtained by oxidation of anthracene.
   [1913 Webster]