Aromatic hydrocarbons are a class of chemical substances which are characterized by having molecular structures which are called benzene rings. The chemically simplest aromatic hydrocarbon is benzene, and the structure of this hydrocarbon lent its name to the benzene ring. Many aromatic hydrocarbons are toxic, and they are unfortunately among the most widespread of organic pollutants.

A hydrocarbon is any chemical compound which contains only hydrogen and carbon. Some hydrocarbons may also contain traces of impurities, as is the case with some aromatic hydrocarbons. In the instance of aromatic hydrocarbons, these impurities caused distinctive scents, leading chemists to term these compounds “aromatic hydrocarbons.” In fact, not all aromatic hydrocarbons smell; the scent was thought to be linked to the benzene ring, but it is actually caused by impurities. However, the name as stuck, as often happens in science even after new information on a topic has emerged, to minimize confusion.

A benzene ring is a molecular structure which is created when six carbon atoms connect with each other in a linked ring. Each carbon atom has four electrons; two electrons link up with neighboring carbon atoms, while one goes to a hydrogen atom. The fourth is what is known as a delocalized electron, meaning that it is not directly involved with a specific atom. Benzene rings are often drawn as hexagonal shapes with a circle in the middle to represent these delocalized electrons. Benzene happens to be a particularly toxic form of aromatic hydrocarbon.

When benzene rings link up, they can form a range of aromatic hydrocarbons, including so-called polycyclic aromatic hydrocarbons (PAHs), or polyaromatic hydrocarbons. These aromatic hydrocarbons are created through incomplete combustion, which is why they are so widely distributed in the natural environment. Most manufacturing facilities, for example, utilize combustion in their operations, potentially generating large amounts of PAHs. Some PAHs are extremely toxic, which can lead to serious problems when they have been deposited in mass amounts by human activity.

An aromatic hydrocarbon may also be known in the abbreviated form of AH or as an arene. A wide range of compounds are classified as arenes, and their potential for harm is based on their molecular structure. You undoubtedly interact with a range of aromatic hydrocarbons every day without being aware of it, and depending on your lifestyle and activities, you may also be exposed to harmful arenes, such as benzopyrene, a PAH found in tobacco smoke and tar.