alkaner

Alkanes, sometimes called alkaner in several languages, are a class of saturated hydrocarbons composed only of carbon and hydrogen, with all bonds between carbon atoms single bonds. The general formula for acyclic alkanes is CnH2n+2, where n is the number of carbon atoms. The simplest members are methane (CH4), ethane (C2H6), propane (C3H8) and butane (C4H10).

Chemically, alkanes are relatively unreactive, but they undergo combustion and radical substitutions. Each carbon atom adopts sp3 hybridization and tetrahedral geometry, giving conformations that enable free rotation around C–C bonds. Straight-chain alkanes are called n-alkanes; those with branching are branched alkanes. Cycloalkanes, with formula CnH2n, are a related but distinct class composed of carbon rings.

Physical properties: alkanes are nonpolar, with very limited water solubility and increasing boiling points with increasing molecular weight. Branching lowers boiling points relative to straight-chain isomers. They are typically gases or liquids at room temperature, depending on size, and are flammable.

Reactions: main chemical process is combustion, yielding carbon dioxide and water. In the presence of UV light or radical initiators, alkanes undergo halogenation (chlorination, bromination) via free-radical chain reactions. Under processing, larger alkanes can be cracked into smaller ones; isomerization and reforming convert straight-chain alkanes into branched forms for fuels and chemicals.

Occurrence and uses: alkanes are abundant in natural gas and crude oil. They serve as fuels and as starting materials for petrochemicals, such as synthesis gas, methanol, ethylene and propylene. IUPAC naming of alkanes is based on the number of carbons, with substitutive naming for branched compounds; common names include methane, ethane, propane, butane and their isomers.