1. Aromatic Hydrocarbons

2. A class of fragrant compounds with unique properties
Benzene – the basis of all aromatic compounds
Friedrich August Kekule first proposed the structure of benzene to be a ring with alternating single and double bons
C6H6

3. 1. Alkenes react to decolorize bromine solutions, but benzene does not
Benzene behaves very differently from most compounds that have double bonds
1. Alkenes react to decolorize bromine solutions, but benzene does not
Br2
Color fades
Br2
Color fades
Br2
No reaction – stays reddish brown

4. 2. Alkenes react with cold potassium permanganate to give diols and brown MnO2, benzene does not
KMnO4
Brown color
0°C
KMnO4
Brown color
0°C OH OH
KMnO4
0°C
No reaction, stays purple

5. 3. Alkenes are hydrogenated with a platinum catalyst at room temperature while benzene resists hydrogenation at room temp. (benzene requires heat and pressure to be hydrogenated)
3H2
Pt, Δ, pressure

6. The structure of benzene is not adequately represented by the two Kekule formulas, but is a resonance hybrid of the two
The structure of benzene is better represented by

7. Nomenclature of Aromatic Hydrocarbons
1. Monosubstituted derivatives are named as derivatives of benzene
Ex.

8. Certain monosubstituted structures retain their “common” names
toluene styrene phenol

9. 2. Disubstituted derivatives have their position on the ring designated by the following:
ortho – adjacent positions on the ring
meta – positions separated by one carbon
para – opposite positions
OR…they can be numbered

10. Common name for dimethyl benzenes are xylene

11. 3. Polysubstituted benzenes have their position numbered
Lowest possible numbers are used (don’t forget to alphabetize)
When the common name of a parent compound is used, the number 1 position is always assigned to the carbon bearing the functional group of the parent compound

12. 4. When an aromatic group is a constituent of a much larger chain, it’s sometimes easier to name it as a substituent group
phenyl group benzyl group

13. Name the following structures.

14. 5. Fused ring derivatives of benzene have their positions numbered
naphthalene anthracene
phenanthrene

15. Name the following structures.