Polycyclic aromatic hydrocarbons (PAHs) are a class of organic compounds that consist of two or more fused benzene rings. Unlike benzene, which has a single ring, PAHs have multiple rings that share edges, forming a larger, conjugated system of π-electrons.
Key Features of PAHs:
- Aromaticity: Each ring contributes to a delocalized π-electron system, giving them stability similar to benzene.
- Hydrophobic and Nonpolar: Most PAHs are insoluble in water but soluble in organic solvents.
- Fused Rings: Rings share one or more sides (edges), which differentiates PAHs from simple aromatic compounds.
- Varied Structure: They can be linear, angular, or cluster-shaped depending on how the rings are fused.
Examples of PAHs:
- Naphthalene (two fused rings)
- Anthracene (three linear fused rings)
- Phenanthrene (three angular fused rings)
- Pyrene (four fused rings in a cluster)
Sources:
- Formed during incomplete combustion of organic matter (coal, wood, gasoline, tobacco smoke).
- Present in fossil fuels and some grilled foods.
Importance:
- Environmental: Many PAHs are pollutants and can be toxic, mutagenic, or carcinogenic.
- Industrial: Some are used in dyes, plastics, and semiconductors.
In short, PAHs are like “extended benzene systems,” where multiple rings share edges, making them larger, stable, and often biologically active.