Aromatic compounds Aromatic compounds l Aromatic compounds are

Aromatic compounds

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

Aromatic hydrocarbons l Benzene C 6 H 6 l Methylbenzene C 7 H 8 l Ethylbenzene C 8 H 10

Benzene

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

Sigma bonding in benzene l l 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 l l 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 l l l Physical state: Benzene. methylbenzene and ethylbenzene are liquids Insoluble in water Soluble in non-polar solvents such as cyclohexane

Uses l Methylbenzene is used as an industrial solvent

Range and scope of aromatic chemistry l Pharmaceutical compounds, e. g. Morphine l Herbicides, e. g. Diuron l Detergents, e. g. Sodium dodecylbenzenesulfonate l Dyes, e. g. Martius Yellow

Aromatic acid-base indicators l The acid-base indicators phenolphthalein and methyl orange are also aromatic compounds Phenolphthalein Methyl orange

Aromatic compounds and cancer l Some aromatic compounds are carcinogenic, e. g. Benzene l However, not all aromatic compounds are carcinogenic; aspirin is an example