Polycyclic Aromatic Hydrocarbon
Definition and meaning of Polycyclic Aromatic Hydrocarbon in chemistry.
A polycyclic aromatic hydrocarbon (PAH) is an organic compound composed of two or more aromatic rings fused together in a condensed structure. PAHs contain only carbon and hydrogen atoms arranged in extended conjugated systems.
In more detail
PAHs form primarily through incomplete combustion of fossil fuels and organic matter, making them common byproducts in vehicle exhaust, industrial emissions, and charred foods. They are environmentally persistent compounds that bioaccumulate in fatty tissues. Many PAHs are toxic or carcinogenic; benzo[a]pyrene is a known human carcinogen. The extensive conjugation in PAH structures gives them unusual optical properties and remarkable chemical stability.
Key facts
| Field | Organic Chemistry |
|---|---|
| Simplest PAH | Naphthalene (C10H8) |
| Structure | Two or more fused aromatic rings |
| Environmental concern | Persistent, toxic, often carcinogenic |
Naphthalene (C10H8), consisting of two fused benzene rings, is the simplest PAH and is commonly found in mothballs and coal tar.
Frequently asked questions
What is the difference between PAHs and regular aromatic compounds?
PAHs have two or more fused aromatic rings, whereas aromatic compounds like benzene have a single ring. The fused ring system creates larger conjugated systems with different chemical and physical properties.
How are PAHs harmful to humans?
Some PAHs, particularly benzo[a]pyrene, are carcinogenic and can accumulate in fatty tissues. Exposure typically occurs through inhalation of combustion products or consumption of smoked and grilled foods.