What is an aromatic hydrocarbon?
An aromatic hydrocarbon is a cyclic hydrocarbon with alternating double and single bonds and (4n + 2) π electrons.
The most common example is benzene (n = 1).
Aromatic hydrocarbons are much more stable than their noncyclic counterparts are.
The carbon-carbon bonds in aromatic hydrocarbons are equivalent. They are not alternating double and single bonds with different lengths. They are all the same length and equivalent to each other.
To show this symmetry, the formulas of aromatic hydrocarbons often use a circle to represent the π electrons.
The structures below are all representations of benzene.
Other aromatic hydrocarbons are naphthalene (10 π electrons; n = 2) and anthracene (14 π electrons; n = 3).
Most of the aromatic compounds you will encounter contain six-membered rings.