phenanthrene

Phenanthrene is a polycyclic aromatic hydrocarbon composed of three fused benzene rings. The name phenanthrene is a composite of phenyl and anthracene. In its pure form, it is found in cigarette smoke and is a known irritant, photosensitizing skin to light. Phenanthrene appears as a white powder having blue fluorescence.

The compound with a phenanthrene skeleton and nitrogens at the 4 and 5 positions is known as phenanthroline.Phenanthrene is nearly insoluble in water but is soluble in most organic solvents such as toluene, carbon tetrachloride, ether, chloroform, acetic acid and benzene.A classical phenanthrene synthesis is the Bardhan-Sengupta phenanthrene synthesis.

The first step is an electrophilic aromatic substitution reaction, which is allowed when the diphosphorous pentoxide makes the alcohol a better leaving group. However, no alkenes outside of the initial aromatic ring are created. In the second step of this reaction 9,10-dihydrophenanthrene is oxidized with elemental selenium. The aromatization of six-membered rings by selenium is not clearly understood, but it does produce H2Se.

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.