Profile
Settings
Refer your friends
Sign out
Alkanes, also known as paraffin, are acyclic saturated hydrocarbons. These are composed of carbon and oxygen atoms arranged in the singular tree structure.
Alkanes are compounds that are entirely composed of carbon and hydrogen atoms linked to each other by carbon-carbon single bonds and carbon-hydrogen single bonds.
Alkanes are insoluble in water, for which they are highly polar. The alkanes are a series of open-chain saturated hydrocarbons.
The alkanes are defined as “acyclic branched or unbranched hydrocarbons” by the International Union of Pure and Applied Chemistry (IUPAC).
The carbon atoms of alkane are sp3 hybridised along with 4 sigma bonds. The hydrogen atoms are joined with carbon atoms by a single bond.
The alkane chains are generated by a general chemical formula. The general indication for alkanes is CnH2n+2.
For example,
n = 1 => C1H2(1) +2 = CH4 = Methane
n = 2 =>C2H2(2) +2 = C2H6 = Ethane
n = 3 =>C3H2(3)+2 = C3H8 = Propane
The series of alkanes are generated by the above formula. The “n” represents the number of bonds that the carbon will hold with hydrogen.
The alkanes are divided into three groups: chain alkanes, cycloalkanes, and branched alkanes.
Isomerism in alkanes
Isomerism arises when there comes a situation for an arrangement of the elements. When alkanes form with more than three carbon atoms, then the concept of arranging them arises. This is known as isomerism.
The simplest isomer of an alkane is the one with a single carbon atom, e.g., methane. There occurs no branching of carbon atoms, and all are arranged by a single chain. These kinds of isomers are known as “n-isomers” (“n” stands for normal; normal isomers).
With the increase in the number of carbon atoms, the chains of carbon increase, giving rise to the formation of rings or chains.
C1 – methane, C2 – Ethane, C3 – Propane, C4 – has two isomers – butane and isobutane.
Similarly, the isomerism keeps increasing with each increase in the number of carbon atoms.
In the isomerisation process, the alkanes become branched-chain isomers. They do not lose any carbon or hydrogen atoms; instead, the molecular weight of the compounds remains the same.
Linear alkanes: Straight chain alkanes are also referred to as linear alkanes. A prefix of “n-” is used while naming such alkanes. In the petroleum industry, single-chained or linear alkanes are known as paraffins. The naming of these alkanes is based on the IUPAC nomenclature.
CH3-CH2-CH2-CH3 (n-butane)
CH3-CH2-CH2-CH2-CH3 (n-pentane)
CH3-CH2-CH2-CH2-CH2-CH3 (n-hexane)
Branched alkanes
The compounds with more than three carbon atoms form either straight chains, branched chains, or rings.
Based on the arrangement, there are three kinds of alkanes, straight-chain alkanes, branched-chain alkanes and cycloalkanes.
For the alkanes that form a straight-chain and branched-chain alkane, the general molecular formula is CnH2n+2.
For the alkanes that form a cycloalkane, the general molecular formula is CnH2n.
Physical properties of alkanes
Alkanes don’t have any colour; they’re colourless.
Alkanes that possess the lowest molecular weight are gases, one with intermediate weight are liquids, and the rest are solids.
Alkanes have higher melting points due to Van der Waals forces.
Alkanes also have a higher boiling point.
Alkanes are not polarised by an electric field, due to which they do not conduct electricity.
Alkanes are hydrophobic, i.e., they are insoluble in water.
Alkanes have no odour, i.e., they are odourless.
Alkanes are non-polar solvents.
Alkanes are non-reactive and possess little biological activity.
Alkanes have lower water density and do float on the water surface.
Chemical properties of alkanes
Alkanes are non-reactive.
When exposed to excess oxygen, alkanes undergo a combustion reaction and form carbon dioxide gas and water.
Alkanes undergo halogenation with chlorine and bromine in the presence of ultraviolet rays to form chloride alkanes and bromide alkanes.
Alkanes undergo a combustion reaction with oxygen, which makes them difficult to ignite.
Alkanes undergo a catalytic method that breaks the larger molecules into smaller ones, resulting in the formation of free radicals.
Occurrence of alkanes
Alkanes form a very small portion of the outer atmosphere of many planets like Jupiter, Saturn, Uranus, Neptune.
The traces of methane gas on earth are mostly produced by methanogenic microorganisms. Alkanes with an even number of carbon atoms break easily, which makes it easier for them to get degraded by certain bacteria.
Alkanes are produced in nature by many bacteria, archaea, fungi and many plants.
On a commercial level, natural gas and oil are the most important sources of alkanes.
Due to the insoluble nature of the alkanes, their presence in the ocean or water bodies is nearly negligible. But, under high pressure and low temperature, methanes can undergo crystallisation with water to form methane clathrate, which is a solid form of methane.
Conclusion
Alkanes possess various chemical and physical properties that make them versatile. Due to their properties, alkanes are widely used in many day-to-day purposes.
The aerosol spray and gas burners are made out of propane and butane, which are liquified under low temperatures.
Alkanes with carbon from five to eight, i.e., from pentane to octane, are used in an internal combustion engine.
Methane and ethane are present in natural gas, which is used for cooking and heating and power efficiency.
Alkanes compose the most important raw materials of the chemical industry and are the main constituent of gasoline and lubricating oils.
Alkanes are also used as fertilisers that come from the production of ammonia by the Haber-Bosch process.
