Hydrocarbons

Hydrocarbons are organic compounds composed exclusively of carbon and hydrogen. They are the most abundant class of organic compounds and form the core of fossil fuels, serving as major energy sources and important chemical feedstocks. They occur in crude oil, natural gas, and coal, and are also produced industrially through refining, cracking, and synthesis processes.

Hydrocarbons are commonly classified by structure into aliphatic and aromatic types. Aliphatic hydrocarbons include open-chain (acyclic) and cyclic forms such as cycloalkanes; they encompass saturated alkanes (single bonds), and unsaturated alkenes (double bonds) and alkynes (triple bonds). Aromatic hydrocarbons, or arenes, contain stable ring systems, the most well-known being benzene. Examples include methane, ethane, propane (alkanes); ethene and propene (alkenes); acetylene (alkyne); benzene and toluene (arenes).

Physical properties of hydrocarbons are largely controlled by size and structure. They are generally nonpolar, with low solubility in water and higher solubility in nonpolar solvents. Boiling points tend to increase with molecular weight and decrease with branching. They are typically flammable and range from gases to liquids at room temperature.

Core reactions include combustion (producing carbon dioxide and water), substitution reactions in alkanes, and addition reactions in alkenes and alkynes. Hydrocarbons also serve as polymer precursors, providing feedstocks for plastics, synthetic fibers, and numerous chemicals. They are used as fuels for transportation and heating, as well as solvents and lubricants.

Environmental considerations include greenhouse gas emissions from combustion and ecological impacts of extraction, transport, and spills. Efforts to mitigate effects focus on efficiency, emissions controls, and alternatives to hydrocarbon fuels.