hydrocarbon

A hydrocarbon is an organic compound that contains only the elements carbon and hydrogen. Hydrocarbons are the principal constituents of crude oil and natural gas and serve as important fuels and chemical feedstocks. They form through geological processes that convert ancient biological material into long-chain molecules.

Classification of hydrocarbons typically falls into several categories. Aliphatic hydrocarbons include alkanes (saturated, with single carbon–carbon bonds), alkenes (unsaturated, containing one or more carbon–carbon double bonds), and alkynes (unsaturated, with one or more carbon–carbon triple bonds). Cycloalkanes are saturated cyclic hydrocarbons. Aromatic hydrocarbons are cyclic, conjugated compounds with delocalized electrons; the best-known example is benzene, along with its derivatives.

Physical properties of hydrocarbons vary with molecular size and structure. They are generally nonpolar and hydrophobic, with limited solubility in water and greater solubility in organic solvents. Boiling and melting points tend to increase with increasing carbon number and molecular complexity. They are typically flammable and can exist as gases, liquids, or solids at ambient conditions depending on their size and structure.

Occurrence and uses: natural gas is rich in light hydrocarbons such as methane, while crude oil is a complex mixture of many hydrocarbons of different chain lengths. Major uses include fuels for transportation and heating, and as feedstocks for petrochemical processes to produce plastics, solvents, synthetic fibers, lubricants, and other chemicals.

Reactions: hydrocarbons undergo a range of reactions. Alkanes are relatively unreactive but combust; alkenes, alkynes, and arenes participate in addition or substitution reactions and polymerization. Environmental and safety considerations include flammability, emissions from combustion, and potential ecological impacts from spills or leaks.