Alkanes

Alkanes are a class of hydrocarbons consisting of hydrogen and carbon joined exclusively by single bonds. They are saturated hydrocarbons and form the simplest homologous series in organic chemistry. The general formula for acyclic alkanes is CnH2n+2 (n ≥ 1). The chains may be straight (n-alkanes) or branched; the latter have isomers with the same molecular formula but different structures.

Physical properties: alkanes are nonpolar and generally insoluble in water, but soluble in nonpolar organic solvents. At room temperature, the first few are gases (methane, ethane, propane), butane and higher are liquids or solids. Boiling points rise with molecular weight and branching lowers boiling point relative to straight-chain isomers.

Chemical properties: alkanes are relatively unreactive compared with other hydrocarbon classes; they predominantly undergo combustion to produce CO2 and H2O. They can participate in radical substitution reactions such as halogenation (chlorination, bromination) under UV light to form alkyl halides. Under higher temperatures or catalysts, cracking, reforming, and other refinery processes convert alkanes into lighter or more useful hydrocarbons.

Occurrence and uses: major components of natural gas (methane) and of petroleum fractions. They are widely used as fuels and lubricants; as solvents in some cases; and as feedstocks for petrochemical synthesis, giving olefins, alcohols, and other products through processing.

Examples: methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10), octane (C8H18).