Anthracene is a condensed aromatic hydrocarbon containing three rings. The center of the three rings of anthracene is in a straight line, which is the isomer of phenanthrene. The chemical activity of the 9 and 10 positions in the anthracene molecule is relatively high. It is oxidized with nitric acid to generate 9, 10-anthraquinone, which is an important intermediate for the synthesis of anthraquinone dyes. Anthracene can also act as a conjugated diene in a Diels-Alder reaction with maleic anhydride.