Aromatic compounds

Aromatic compounds

Aromatic compounds are compounds which contain a benzene ring in their molecules

Aromatic hydrocarbons

Benzene C6H6

Methylbenzene C7H8

Ethylbenzene C8H10

Benzene

Benzene molecule

The six carbon-carbon bonds in benzene are identical, intermediate in length between double and single bonds

Sigma bonding in benzene

Six carbon atoms joined to form a hexagonal planar ring.

Each carbon has four valence electrons One of these is used to form a bond with a

hydrogen atom. Two other electrons are used to form sigma

bonds with the carbon atoms on either side.

What the circle means

The 6 valence electrons not involved in sigma bonding are shared between the six carbon atoms in the molecule

not localised into 3 double bonds For convenience the C and H atoms are not

shown Ring in centre indicates a delocalised pi bond

Methylbenzene

Ethylbenzene

Physical properties

Physical state: Benzene. methylbenzene and ethylbenzene are liquids

Insoluble in water Soluble in non-polar solvents such as

cyclohexane

Uses

Methylbenzene is used as an industrial solvent

Range and scope of aromatic chemistry

Pharmaceutical compounds, e.g. Morphine

Herbicides, e.g. Diuron

Detergents, e.g. Sodium dodecylbenzenesulfonate

Dyes, e.g. Martius Yellow

Aromatic acid-base indicators

The acid-base indicators phenolphthalein and methyl orange are also aromatic compounds

Phenolphthalein Methyl orange

Aromatic compounds and cancer

Some aromatic compounds are carcinogenic, e.g. Benzene

However, not all aromatic compounds are carcinogenic; aspirin is an example