Aromatic hydrocarbon

An aromatic hydrocarbon contains only carbon and hydrogen and has a conjugated ring system with delocalized electrons that satisfies aromaticity criteria.

Aromaticity: A property of cyclic, conjugated systems whose delocalized electrons produce characteristic stability and bonding. It is the defining electronic property that makes an aromatic hydrocarbon aromatic.
Benzene: A six-carbon aromatic hydrocarbon with formula C6H6 and a planar ring of delocalized π electrons. Its ring is the simplest and most familiar model of aromatic hydrocarbon bonding.
Polycyclic aromatic hydrocarbon: A hydrocarbon containing two or more fused aromatic rings. Fused rings extend aromatic structure and include many persistent combustion products.
Aliphatic hydrocarbon: A hydrocarbon that is not aromatic, including open-chain and nonaromatic cyclic structures. It contrasts ring-delocalized aromatic structures with hydrocarbons lacking aromaticity.
Michael Faraday: An English scientist whose 1825 analysis of illuminating gas led to the discovery of benzene. His isolation and analysis of benzene began the history of its chemistry.
Conjugated system: A sequence of adjacent orbitals that permits electron delocalization across multiple atoms. Conjugation provides the connected orbital pathway needed for ring-wide electron sharing.
Aromatic stabilization: The energetic stabilization associated with cyclic electron delocalization in an aromatic system. Delocalization gives aromatic hydrocarbons distinctive stability relative to suitable nonaromatic comparators.
Toluene: An aromatic hydrocarbon consisting of a benzene ring bonded to a methyl group. Toluene is a widely used solvent and an important petrochemical feedstock.
Cycloalkene: A nonaromatic cyclic hydrocarbon containing at least one carbon–carbon double bond. A ring and double bond alone do not make a hydrocarbon aromatic.
August Kekulé: A German chemist who proposed a cyclic structure for benzene in the nineteenth century. His ring model helped make the unusual composition of benzene structurally intelligible.

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