C6H4.C2H2.C6H4

from The Collaborative International Dictionary of English v.0.48

Anthracene \An"thra*cene\, n. [Gr. 'a`nqrax coal.] (Chem.)
   A solid hydrocarbon, {C6H4.C2H2.C6H4}, which accompanies
   naphthalene in the last stages of the distillation of coal
   tar. Its chief use is in the artificial production of
   alizarin. [Written also {anthracin}.]
   [1913 Webster]