Aromatic Compound
Definition
Molecules with special ring structures and delocalized electrons, like benzene, that are unusually stable and have a distinctive chemistry.
Technical definition
Aromatic compounds contain a planar ring with a conjugated pi system satisfying Huckel's rule of 4n+2 pi electrons. The delocalization grants exceptional stability, so they undergo substitution rather than addition reactions.
Example
Benzene (C6H6) resists the addition reactions that alkenes undergo eagerly. Instead it undergoes electrophilic substitution, preserving its aromatic ring.
Common confusion
Aromatic does not mean fragrant: it is a structural term. Many aromatics do smell, but the name refers to the electron arrangement, not the odor.