Polycyclic aromatic hydrocarbons (PAHs, also
polyaromatic hydrocarbons) are
hydrocarbons—
organic compounds containing only carbon and hydrogen—that are composed of multiple
aromatic rings (organic rings in which the electrons are
delocalized). Formally, the class is further defined as lacking further branching
substituents off of these ring structures.
Polynuclear aromatic hydrocarbons (PNAs) are a subset of PAHs that have fused
aromatic rings, that is, rings that share one or more sides. Though poly- in these cases literally means "many", there is precedence in nomenclature for beginning this class and subclass with the two ring cases, where
naphthalene would therefore be considered a simple example; beginning at three rings, examples include
anthracene and
phenanthrene.
