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Hydrocarbon


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http://upload.wikimedia.org/wikipedia/commons/thumb/5/58/methane-3d-balls.png/240px-methane-3d-balls.png

Ball-and-stick model of the methane molecule, CH4. Methane is part of a homologous series known as the alkanes, which contain single bonds only.

In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon.[1] Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls.[2] Aromatic hydrocarbons (arenes), alkanes, alkenes, cycloalkanes and alkyne-based compounds are different types of hydrocarbons.

The majority of hydrocarbons found on Earth naturally occur in crude oil, where decomposed organic matter provides an abundance of carbon and hydrogen which, when bonded, can catenate to form seemingly limitless chains.[3][4]


Contents


[hide]

  • 1 Types of hydrocarbons

    • 1.1 General properties

    • 1.2 Simple hydrocarbons and their variations

  • 2 Usage

  • 3 Poisoning

  • 4 Reactions

    • 4.1 Substitution Reaction

    • 4.2 Addition Reaction

    • 4.3 Combustion

      • 4.3.1 Petroleum

      • 4.3.2 Bioremediation

  • 5 See also

  • 6 References

  • 7 Bibliography

  • 8 External links

Types of hydrocarbons[edit]


The classifications for hydrocarbons, defined by IUPAC nomenclature of organic chemistry are as follows:

  1. Saturated hydrocarbons (alkanes) are the simplest of the hydrocarbon species. They are composed entirely of single bonds and are saturated with hydrogen. The general formula for saturated hydrocarbons is CnH2n+2 (assuming non-cyclic structures).[5] 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.[6] As given in the example of 3-methylhexane and its higher homologues, branched hydrocarbons can be chiral.[7] Chiral saturated hydrocarbons constitute the side chains of biomolecules such as chlorophyll and tocopherol.[8]

  2. 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).[9] Those containing triple bonds are called alkynes, with general formula CnH2n-2.[10]

  3. Cycloalkanes are hydrocarbons containing one or more carbon rings to which hydrogen atoms are attached. The general formula for a saturated hydrocarbon containing one ring is CnH2n.[6]

  4. Aromatic hydrocarbons, also known as arenes, are hydrocarbons that have at least one aromatic ring.

Hydrocarbons can be gases (e.g. methane and propane), liquids (e.g. hexane and benzene), waxes or low melting solids (e.g. paraffin wax and naphthalene) or polymers (e.g. polyethylene, polypropylene and polystyrene).

General properties[edit]


Because of differences in molecular structure, the empirical formula remains different between hydrocarbons; in linear, or "straight-run" alkanes, alkenes and alkynes, the amount of bonded hydrogen lessens in alkenes and alkynes due to the "self-bonding" or catenation of carbon preventing entire saturation of the hydrocarbon by the formation of double or triple bonds.

This inherent ability of hydrocarbons to bond to themselves is known as catenation, and allows hydrocarbon to form more complex molecules, such as cyclohexane, and in rarer cases, arenes such as benzene. This ability comes from the fact that the bond character between carbon atoms is entirely non-polar, in that the distribution of electrons between the two elements is somewhat even due to the same electronegativity values of the elements (~0.30), and does not result in the formation of an electrophile.

Generally, with catenation comes the loss of the total amount of bonded hydrocarbons and an increase in the amount of energy required for bond cleavage due to strain exerted upon the molecule;in molecules such as cyclohexane, this is referred to as ring strain, and occurs due to the "destabilized" spatial electron configuration of the atom.

In simple chemistry, as per valence bond theory, the carbon atom must follow the "4-hydrogen rule", which states that the maximum number of atoms available to bond with carbon is equal to the number of electrons that are attracted into the outer shell of carbon. In terms of shells, carbon consists of an incomplete outer shell, which comprises 4 electrons, and thus has 4 electrons available for covalent or dative bonding.

Hydrocarbons are hydrophobic like lipids.

Some hydrocarbons also are abundant in the solar system. Lakes of liquid methane and ethane have been found on Titan, Saturn's largest moon, confirmed by the Cassini-Huygens Mission.[11] Hydrocarbons are also abundant in nebulae forming polycyclic aromatic hydrocarbon (PAH) compounds.[12]


Simple hydrocarbons and their variations[edit]


Number of
carbon atoms


Alkane (single bond)

Alkene (double bond)

Alkyne (triple bond)

Cycloalkane

Alkadiene

1

Methane

-

-

-

-

2

Ethane

Ethene (ethylene)

Ethyne (acetylene)





3

Propane

Propene (propylene)

Propyne (methylacetylene)

Cyclopropane

Propadiene (allene)

4

Butane

Butene (butylene)

Butyne

Cyclobutane

Butadiene

5

Pentane

Pentene

Pentyne

Cyclopentane

Pentadiene (piperylene)

6

Hexane

Hexene

Hexyne

Cyclohexane

Hexadiene

7

Heptane

Heptene

Heptyne

Cycloheptane

Heptadiene

8

Octane

Octene

Octyne

Cyclooctane

Octadiene

9

Nonane

Nonene

Nonyne

Cyclononane

Nonadiene

10

Decane

Decene

Decyne

Cyclodecane

Decadiene
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