Hydrocarbon

Hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are generally colourless and hydrophobic with only weak odours. Because of their diverse molecular structures, it is difficult to generalize further.

Hydrocarbons are generally of low toxicity, hence the widespread use of gasoline and related volatile products. Aromatic compounds such as benzene are narcotic and chronic toxins and are carcinogenic.

Certain rare polycyclic aromatic compounds are carcinogenic. Hydrocarbons are highly flammable.

The vast majority of hydrocarbons found on Earth occur in crude oil, petroleum, coal, and natural gas.

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The classifications for hydrocarbons are:

Saturated hydrocarbons are the simplest of the hydrocarbon species. They are composed entirely of single bonds and are saturated with hydrogen. The formula for acyclic saturated hydrocarbons (i.e., alkanes) is CnH2n+2.  The most general form of saturated hydrocarbons is CnH2n+2(1-r), where r is the number of rings.

Those with exactly one ring are the cycloalkanes. Saturated hydrocarbons are the basis of petroleum fuels and are found as either linear or branched species. Substitution reaction is their characteristics property (like chlorination reaction to form chloroform).

Hydrocarbons with the same molecular formula but different structural formulae are called structural isomers.  As in 3-methylhexane and its higher homologues, branched hydrocarbons can be chiral.  Chiral saturated hydrocarbons constitute the side chains of biomolecules such as chlorophyll and tocopherol.

Unsaturated hydrocarbons have one or more double or triple bonds between carbon atoms. Those with double bond are called alkenes. Those with one double bond have the formula CnH2n (assuming non-cyclic structures). Those containing triple bonds are called alkyne. Those with one triple bond have the formula CnH2n−2.

Aromatic hydrocarbons, also known as arenes, are hydrocarbons that have at least one aromatic ring. 10% of total nonmethane organic carbon emission are aromatic hydrocarbons from the exhaust of gasoline-powered vehicles.

Most anthropogenic emissions of hydrocarbons are from the burning of fossil fuels including fuel production and combustion. Natural sources of hydrocarbons such as ethylene, isoprene, and monoterpenes come from the emissions of vegetation

The predominant use of hydrocarbons is as a combustible fuel source. Methane is the predominant component of natural gas. The C6 through C10 alkanes, alkenes and isomeric cycloalkanes are the top components of gasoline, naphtha, jet fuel and specialized industrial solvent mixtures.

With the progressive addition of carbon units, the simple non-ring structured hydrocarbons have higher viscosities, lubricating indices, boiling points, solidification temperatures, and deeper color. At the opposite extreme from methane lie the heavy tars that remain as the lowest fraction in a crude oil refining retort.

Some large-scale non-fuel applications of hydrocarbons begins with ethane and propane, which are obtained from petroleum and natural gas.

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