Hydrocarbon definition and examples
An organic compound containing carbon and hydrogen in entirely in the molecule is known as a hydrocarbon. Therefore the main sources of liquid hydrocarbons are crude oil, natural gas, coal, and other natural resources.
Hydrocarbons in crude oil
But the crude petroleum oil is a mixture of organic compounds mainly hydrocarbons. Hence the crude petroleum oil contains mainly three types of hydrocarbon.
- Alkanes containing straight and branched-chain
- Cycloalkanes or naphthenes
- Aromatic hydrocarbons
But in addition to hydrocarbon, there are also present compounds containing O2, N2, S, and metallic compounds.
Hydrocarbon in natural gas
The terms natural gas used for the total quantity of gas present in liquid petroleum. But the main component of natural gas varies according to the source and it consists chiefly of the first six alkanes.
Therefore the percentage of alkanes decreases with increasing molecular weight. But the other gases such as water vapor, H2, N2, CO2, H2S also present in natural gases and vary with the locality of occurrence.
First six alkanes formula and names
|Alkanes||Molecular formula||Molecular weight|
|Methane||CH4||16 gm mol-1|
|Ethane||C2H6||30 gm mol-1|
|Propane||C3H8||44 gm mol-1|
|Butane||C4H10||58 gm mol-1|
|Pentane||C5H12||72 gm mol-1|
|Hexane||C6H14||86 gm mol-1|
Structure of hydrocarbon
It occurs in nature, contains different structures. Thus according to the structure, they are mainly two types
- Cyclic or closed chain
The saturated and unsaturated compounds
The organic compounds which contain two or more carbon atoms linking by the only a single chemical bond are called unsaturated compounds.
Thus CH3CH3, CH3CH2OH, CH3CHO are examples of unsaturated compounds. But alkanes and cycloalkanes are the examples of unsaturated hydrocarbon because it forms by only carbon and hydrogen.
Therefore the compound contains at least one pair of adjacent carbon atoms linked by multiple bonds, then the compounds are said to be unsaturated compounds.
- If it contains a double bond between adjacent carbon atoms known as alkenes.
- But when a triple bond between adjacent carbon atoms known as alkynes.
- In CH3CHO, it contains multiple bonds between adjacent carbon and an oxygen atom. But the double bond between carbon and oxygen is not considered for unsaturation.
Alkanes alkenes and alkynes
- Alkanes or paraffin are the saturated hydrocarbons that occur naturally and crude petroleum oil.
- Alkenes or olefins are also the compounds that contain one double bond or olefinic bond. Thus a number of low molecular weight alkenes prepared by creaking petroleum crude oil. But for the production of alkenes having high molecular weight we use Wax or Fischer Tropsch wax method.
- Alkynes are the compounds that contain one triple bond and this bond is known as the acetylenic bond. Hence many alkynes have been found in nature and use broadly in our civilization.
If the compounds contain closed rings with carbon atoms, then the compounds are collectively known as carbocyclic or homocyclic compounds.
But if it resembles the aliphatic compounds are called alicyclic compounds.
Cycloalkanes and cycloalkenes
The saturated cyclic hydrocarbons take the names of the corresponding open-chain compounds, proceeds by the prefix cyclo.
Thus these compounds collectively called cycloparaffins or cycloalkanes. When the alicyclic hydrocarbon is unsaturated, then this hydrocarbon called cycloalkenes.
Aliphatic and aromatic hydrocarbons
With the development of basic chemistry, organic compounds were mainly in three types
- Aliphatic hydrocarbons
- Aromatic hydrocarbons
- Heterocyclic hydrocarbons
The aliphatic name was given because this class is obtained from fatty acids but today it is known as open-chain compounds. Therefore several compounds coming from the natural sources with a definite order and a pleasant smell are known as aromatic compounds.
But the aromatic name obtained from the Greek word aroma means fragrant smell. Hence details examination shows that the aromatic compounds show the property of aromaticity.
Therefore most of the aromatic compounds related to benzene or its derivative. Thus cyclic benzenoid compound also an aromatic compound. But the properties of these compounds totally different from alicyclic compounds.
Examples of aliphatic and aromatic hydrocarbons
Cracking of hydrocarbon
The thermal decomposition of organic compounds is known as pyrolysis but if it applied to the hydrocarbons or alkanes is known as creaking.
Thus alkanes are decomposed to lower alkane by heating 5000C to 6000C. Therefore the product obtained from a given alkane depends on
- Structure of the alkane
- Applied pressure
- The catalyst used
Hence the thermal decomposition of decane given octane and ethene.
But using suitable catalysts, alkanes containing six or more carbon atoms are cyclized.
Thus when petroleum oil creaked, most of the hydrocarbons are produced. Therefore most important hydrocarbon are those containing up to four carbon atom which is methane, ethane, ethylene, propane, butane, butane and isobutene.