# Polynuclear Hydrocarbons

What are Polynuclear Hydrocarbons?

These are uncharged, lipophilic molecules made up of fused multiple aromatic rings. They contain carbon and hydrogen atoms only. The 2, 3, and 4 rings containing polycyclic aromatic hydrocarbons (PNH) are volatile and exist in the gas phase while larger size molecules exist as colorless, pale yellow, pale green, or white colored solids.

Examples include,

These compounds are primarily found in natural sources like coal and petroleum products. They are generated by burning garbage, wood, and incomplete combustion of fossil fuels, and are also present in cigarette smoke.

They are typically found as complex mixtures. Combustion at a lower temperature (e.g., cigarette smoke) generates low molecular weight PNHS whereas a high-temperature industrial process typically generates high molecular weight PNHS.

## Classification of Polynuclear Hydrocarbons

They are classified as:

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