17.1 : 芳香族化合物：概述

Aromatic compounds are hydrocarbons with conjugated π bonds enclosed in a ring. Benzene and its derivatives are the best-known examples of aromatic compounds.

Originally, benzene derivatives were isolated from natural oils produced by plants and trees and were called 'aromatic' due to their distinctive odor.

For example, benzaldehyde from almonds and cherries, toluene from Tolu balsam, and eugenol from clove have distinct odors.

Over time, the term aromatic has continued to describe all benzene derivatives, irrespective of whether they are fragrant or not. For example, the pain reliever aspirin contains acetylsalicylic acid, an odorless aromatic compound.

Structurally, aromatic compounds are highly unsaturated hydrocarbons and exhibit different chemical behavior from alkenes, alkynes, and open-chain polyenes.

The primary sources of simple aromatic compounds are coal tar and petroleum.

Fractional distillation of coal tar yields many aromatic compounds such as benzene, toluene, xylene, naphthalene, and others.

Similarly, during petroleum refining, alkanes are converted to aromatic compounds.