Chapter 4: Aromatic Compounds

The word “aromatic” refers to the pleasant odour from some resources, such as flowers, trees, cinnamon buns, etc.  In the early history of organic chemistry, it was found that a group of compounds usually isolated from natural resources, such as oil, and plants, have such a pleasing sweet smell, and they all have the structure unit of the benzene ring. The word “aromatic compound” was used for such a group of compounds containing benzene rings. The meaning of “aromatic” in contemporary organic chemistry, however, has been further extended to compounds that have benzene rings, fused benzene rings, or cyclic structures that have similar properties as benzene. The pleasant smell is not the necessary common feature for aromatic compounds anymore, instead, they all share similar chemical stability and reactivity because of their unique electronic structure features.

The benzene ring is still the most characteristic structure for aromatic compounds. It can usually be represented in different ways.

We will start with the properties of benzene and derivatives, and then introduce aromatic compounds with other cyclic structures.