hydrocarbon (redirected from Hydrocarbons)

hydrocarbon (hī'drōkär`bən), any organic compound composed solely of the elements hydrogen and carbon. The hydrocarbons differ both in the total number of carbon and hydrogen atoms in their molecules and in the proportion of hydrogen to carbon. The hydrocarbons can be divided into various homologous series. Each member of such a series shows a definite relationship in its structural formula to the members preceding and following it, and there is generally some regularity in changes in physical properties of successive members of a series. The alkanes are a homologous series of saturated aliphatic hydrocarbons. The first and simplest member of this series is methane, CH₄; the series is sometimes called the methane series. Each successive member of a homologous series of hydrocarbons has one more carbon and two more hydrogen atoms in its molecule than the preceding member. The second alkane is ethane, C₂H₆, and the third is propane, C₃H₈. Alkanes have the general formula C_nH_2n+2 (where n is an integer greater than or equal to 1). Generally, hydrocarbons of low molecular weight, e.g., methane, ethane, and propane, are gases; those of intermediate molecular weight, e.g., hexane, heptane, and octane, are liquids; and those of high molecular weight, e.g., eicosane (C₂₀H₄₂) and polyethylene, are solids. Paraffin is a mixture of high-molecular-weight alkanes; the alkanes are sometimes called the paraffin series. Other homologous series of hydrocarbons include the alkenes and the alkynes. The various alkyl derivatives of benzene are sometimes referred to as the benzene series. Many common natural substances, e.g., natural gas, petroleum, and asphalt, are complex mixtures of hydrocarbons. The coal tar obtained from coal by coking is also a mixture of hydrocarbons. Natural gas, petroleum, and coal tar are important sources of many hydrocarbons. These complex mixtures can be refined into simpler mixtures or pure substances by fractional distillation. During the refining of petroleum, one kind of hydrocarbon is often converted to another, more useful kind by cracking. Useful hydrocarbon mixtures include cooking gas, gasoline, naphtha, benzine, kerosene, paraffin, and lubricating oils. Many hydrocarbons are useful as fuels; they burn in air to form carbon dioxide and water. The hydrocarbons differ in chemical activity. The alkanes are unaffected by many common reagents, while the alkenes and alkynes are much more reactive, as a result of the presence of unsaturation (i.e., a carbon-carbon double or triple bond) in their molecules. Many important compounds are derived from hydrocarbons, either by substitution or replacement by some other chemical group or element of one or more of the hydrogen atoms of the hydrocarbon molecule, or by the addition of some element or group to a double or triple bond (in an unsaturated hydrocarbon). Such derivatives include alcohols, aldehydes, ethers, carboxylic acids, and halocarbons.

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hydrocarbon

Any of a class of organic compounds composed only of carbon and hydrogen. The carbon atoms form the framework, and the hydrogen atoms attach to them. Hydrocarbons, the principal constituents of petroleum and natural gas, serve as fuels, lubricants, and raw materials for production of plastics, fibres, rubbers, solvents, explosives, and industrial chemicals. All burn to carbon dioxide and water with enough oxygen or to carbon monoxide without it. The two major categories are aliphatic, with the carbon atoms in straight or branched chains or in nonaromatic rings, and aromatic (see aromatic compound). Aliphatic compounds may be saturated (paraffins) or, if any carbon atoms are joined by double or triple bonds, unsaturated (e.g., olefins, alkenes, alkynes). All but the simplest hydrocarbons have isomers (see isomerism). Ethylene, methane, acetylene, benzene, toluene, and naphthalene are hydrocarbons.

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hydrocarbon

any organic compound containing only carbon and hydrogen, such as the alkanes, alkenes, alkynes, terpenes, and arenes

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hydrocarbon [¦hī·drə′kär·bən]

(organic chemistry)

One of a very large group of chemical compounds composed only of carbon and hydrogen; the largest source of hydrocarbons is from petroleum crude oil.