benzenes

Benzene and related benzenoid compounds form a family of aromatic hydrocarbons with a characteristic six-membered ring. The parent compound, benzene (C6H6), is a planar ring in which six carbon atoms are sp2 hybridized and carry one hydrogen each. The ring contains a delocalized system of six pi electrons, giving rise to aromatic stability. In simple representations the ring is shown with alternating single and double bonds, but the true structure is a resonance hybrid with equal bond lengths.

Benzenes occur naturally in trace amounts in crude oil and fossil fuels and have historically been derived from coal tar. Industrial production today primarily uses catalytic reforming of refinery fractions and related processes that generate benzene-containing streams from fossil-fuel feedstocks. Benzene serves as a foundational building block in the chemical industry, converting into a wide range of compounds such as cyclohexane, phenol, aniline, and various substituted benzenes.

Reactivity is governed by aromatic substitution rather than addition. Typical reactions include nitration, sulfonation, halogenation, and Friedel–Crafts alkylation or acylation. Hydrogenation of benzene yields cyclohexane under higher pressure and temperature conditions. Many important industrial chemicals and polymers are prepared from benzene or from benzene derivatives, including styrene, phenol, and nylon precursors.

Safety and environmental concerns are significant. Benzene is highly flammable and toxic; long-term exposure is linked to an increased risk of leukemia and other disorders. Consequently, handling and emissions are tightly regulated, and substitutes or process controls are employed to minimize exposure in industrial settings.