CHEM 121 glossary
Aromatic ring
A flat, fully conjugated ring such as benzene, in which a p orbital on every ring atom overlaps its neighbours all the way around, so the π electrons (6 in benzene) are delocalized over the whole ring. This delocalization makes aromatic rings unusually stable; they are drawn as a hexagon with three alternating double bonds.
Naphthalene: two fused aromatic rings, 10 π electrons.
Example
Aspirin, ibuprofen and styrene each contain one benzene ring. Naphthalene, , is two aromatic rings sharing one edge, with 10 delocalized π electrons.