Phenanthrene is a polycyclic aromatic hydrocarbon composed of three fused benzene rings. The name phenanthrene is a composite of phenyl and anthracene. It provides the framework for the Steroids. In its pure form, it is found in cigarette smoke and is a known irritant, photosensitising skin to light.
The compound with a phenanthrene skeleton and nitrogens at the 4 and 5 position is known as phenanthroline or 4,5-diazaphenanthrene (IUPAC name).
Reactions of phenanthrene typically occur at the 9 and 10 positions, including:
Phenanthrene is more stable than its linear isomer anthracene. A classic and well established explanation is based on Clar's rule. A novel theory invokes so-called stabilizing hydrogen-hydrogen bonds between the C4 and C5 hydrogen atoms.