Question

What do aromatic compounds contain?

Answer 1

A benzene, or so-called aryl ring, `C_6H_6`, that may be substituted with heteratoms or hydrocarbyl groups.

Explanation:

Aromatic chemistry is not confined solely to the phenyl ring; there are examples of other compounds, both inorganic and organic that we would properly describe as aromatic.

What characterizes benzene as aromatic as is the presence of `6` `pi` electrons constrained in a ring, to give a carbocycle. Some chemists may draw this as `"1,3,5-cyclohexatriene"`; younger chemists may write this as a hexagon with a circle circumscribed within; the `6` `pi` electrons are delocalized around the ring, and are not associated with any particular carbon.

This benzene ring is a ubiquitous feature of organic compounds because while its unsaturation means that it is reactive, the carbocycle tends to retain its structural integrity upon reaction in that the ring undergoes aromatic electrophilic substitution, that is distinct from olefin chemistry.