1. 9.4 Aromatics
The compounds we have been studying so far are all known as aliphatic hydrocarbons.
A particular group of cyclic compounds are called arenes or aromatic compounds.
This term is used particularly with reference to benzene.
Benzene is the simplest
of the arenes, C6H6

2. Benzene
The benzene molecule is a six membered carbon ring with a hydrogen atom attached to each carbon.
This means that there is an extra bonding electron on each carbon atom to participate in a double bond.
In fact, due to the phenomenon of resonance these electrons are shared equally by the carbon atoms and a very flat stable ring structure is formed.

3. The structure of benzene can be represented by one of the following diagrams:
At each point of the hexagon is a carbon atom with a hydrogen atom attached, while the circle represents the double bonds between adjacent carbons.

4. Substituted Benzenes
The hydrogen atoms on the benzene ring may be substituted by alkyl groups.
The benzene ring may itself be a substituent on a longer hydrocarbon chain.
In this case the benzene ring is called a phenyl group.

5. Example 1 It is a solvent used in glues and lacquers.
It is preferred to benzene because it is not carcinogenic.
Methylbenzene
(toluene)

6. Other mono-substituted benzenes
ethylbenzene
propylbenzene

7. Example 2
Used as a solvent in the printing, rubber and leather industries.
1,2-dimethylbenzene
(or xylene).

8. There are two other possible isomers of this compound:
1,3-dimethybenzene
1,4-dimethylbenzene

9. Example 3
Here the benzene is a substituent on another hydrocarbon chain.
2-phenylpentane.

10. Aromatic Hydrocarbons Worksheet

11. Aromatic Hydrocarbons Worksheet

12. Aromatic Hydrocarbons Worksheet