Hydrocarbon definition and examples
An organic compound containing carbon and hydrogen in entirely in the molecule is known as a hydrocarbon. The main sources of hydrocarbons are crude oil, natural gas, coal, and other natural resources.
Hydrocarbon in crude oil
Crude petroleum oil mainly the gasses occurring naturally in forms of liquified and solid which dissolved in or separated from the liquid. But the crude petroleum oil is a mixture of organic compounds mainly hydrocarbons.
Thus the crude petroleum oil contains mainly three types of hydrocarbon.
- Alkanes containing straight and branched-chain.
- Cycloalkanes or naphthenes.
- Aromatic hydrocarbon.
But in addition to hydrocarbon, there are also present compounds containing oxygen, nitrogen, sulfur, and metallic constituents.
Hydrocarbon in natural gas
The terms natural gas used for the total quantity of gas associated with liquid petroleum gas.
Thus the main component of natural gas varies according to the source and it consists chiefly of the first six alkanes. But the percentage of alkanes decreases with increasing molecular weight.
The other gases such as water vapor, hydrogen, nitrogen, CO2, H2S also present in natural gases and varies 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 hydrocarbons
Hydrocarbons which occur in nature, contain different structure. Thus according to the structure, they are mainly two types
- Open-chain compounds.
- Cyclic or closed chain compounds.
The saturated and unsaturated compounds
The organic compounds which contain two or more carbon atoms linking by only single bonds are called unsaturated compounds.
Thus ethane, n-propanol, acetaldehyde are examples of unsaturated compounds. But alkanes and cycloalkanes are the examples of unsaturated hydrocarbon because it forms by only carbon and hydrogen.
If the compound contains at least one pair of adjacent carbon atoms linked by multiple bonds, then the compounds are said to be unsaturated compounds.
- The unsaturated compound contains a double bond between adjacent carbon atoms known as alkanes.
- But the unsaturated hydrocarbon contains a triple bond between adjacent carbon atoms known as alkenes.
- Thus if we consider acetaldehyde, 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 unsaturated hydrocarbons 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 unsaturated hydrocarbons that contain one triple bond and this chemical 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 of carbon atoms, then the compounds are collectively known as carbocyclic or homocyclic compounds.
But the compounds that resemble the aliphatic compounds are called alicyclic compounds.
Cycloalkanes and cycloalkenes
The saturated monocyclic hydrocarbons take the names of the corresponding open-chain saturated hydrocarbons, proceeds by the prefix cyclo. Thus these saturated monocyclic compounds are collectively called cycloparaffins or cycloalkanes.
When the alicyclic hydrocarbon is unsaturated, then this hydrocarbon called cycloalkenes.
Aliphatic and aromatic hydrocarbons
With the development of organic chemistry, organic compounds were classified mainly in three classes.
The aliphatic name was given because the first compounds from this class obtained from fatty acids. Today this is known as open chain compounds.
Thus there are several compounds coming from the natural sources with a definite order and a pleasant smell. These compounds are called aromatic compounds. But the aromatic name obtained from the Greek word aroma means fragrant smell.
Thus details examination shows that the saturated aromatic compounds show the property of aromaticity. But most of the aromatic compounds related to benzene or a derivative of benzene.
The cyclic benzenoid compound also aromatic compound. But the properties of these compounds are totally different from alicyclic compounds.
Examples of aromatic hydrocarbons
|Saturated hydrocarbon||Unsaturated hydrocarbon|
Cracking of hydrocarbon
The thermal decomposition of organic compounds is known as pyrolysis but pyrolysis applied to the hydrocarbon alkane is known as creaking.
Thus alkanes are decomposing to lower alkane by heating 5000C to 6000C. But the product obtained by this decomposition of given alkanes depends on
- Structure of the alkanes.
- Pressure applied for this decomposition.
- The catalyst used for this decomposition.
So the thermal decomposition of decane given octane and ethene.
But using suitable catalysts, alkanes containing six or more carbon atom catalytically cyclized.
Thus when petroleum oil creaked, most of the hydrocarbon produced. But most important hydrocarbons are those containing up to four carbon atom which is methane, ethane, ethylene, propane, butane, butane and isobutene.