An
aromatic hydrocarbon or
arene (or sometimes
aryl hydrocarbon) is a
hydrocarbon with
sigma bonds and delocalized
pi electrons between carbon atoms forming rings. The term 'aromatic' was assigned before the physical mechanism determining
aromaticity was discovered; the term was coined as such simply because many of the compounds have a sweet or pleasant odour. The configuration of six carbon atoms in aromatic compounds is known as a benzene ring, after the simplest possible such hydrocarbon,
benzene. Aromatic hydrocarbons can be
monocyclic (MAH) or
polycyclic (PAH).