Chapter 11 : Arenes and Aromaticity

Larger systems of benzene rings fused together are also well known. These are the polyaromatic hydrocarbons (sometimes referred PAHs). A collection of images of some common systems are shown below. The planarity of these extended π systems can be seen when the JSMOL images are rotated. Make sure you test out the Huckel rule on each of them and check by holding the mouse over the line drawing.
The chemistry of these systems is similar to that of the parent benzene, but they are usually more reactive than benzene. Evidence for this can be seen in the resonance energy data which shows that their resonance energies are less than the same number of isolated benzenes.

 

Compound Name	Line Drawing	3D Model	Resonance Energy
Benzene			152 kJ/mol 36 kcal/mol
Naphthalene			255 kJ/mol 61 kcal/mol
Anthracene			347 kJ/mol 83 kcal/mol
Phenanthrene			381 kJ/mol 91 kcal/mol

© Dr. Ian Hunt, Department of Chemistry