Aromatic refers to the compounds that contain a benzene ring. Benzene the simplest and most widely known aromatic compound, contains six membered ring and three double bonds. Each carbon of the ring is also bonded to a hydrogen atom, so the molecular formula of benzene is C6H6.

Th equivalent nature of carbon-carbon bonds in benzene is addressed by considering the correct bonding structure for benzene to be an average of the two “triene” structures. related to this “average” structure situation is the concept that electrons associated with the double bonds are not held in between specific carbon atoms; instead they are free to move around the carbon ring. Thus the real structures between two triene structures is a situation in which all carbon-carbon bonds are equivalent. They are neither double nor single but somewhere in between, called resonating structures.

In the resonating structures below we see two equivalent structures of benzene whereas a single equivalent structure of benzene is the one below the resonating structures.

n the above “circle in the ring” structure for benzene, the circle denotes the electrons associated with the double bonds that move around the ring. each carbon atom in the ring can be considered to participate in one pure covalent conventional C-H bonds and two delocalized covalent bonds between two adjacent carbon atoms.

This delocalized bond is what causes benzene and its derivatives to be resistant to addition reactions. This notation is called AROMATIC RING SYSTEM which is highly unsaturated ring system in which both localized and delocalized bonds are present.

Aromatic compounds with more than one ring: Some aromatic compounds contain two or more benzene rings joined together. There are two different aromatic hydrocarbons with three benzene rings, named naphthalene, phenanthrene and anthracene.

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