Chemical Properties Of Alkanes

An alkane is an acyclic saturated hydrocarbon in organic chemistry, commonly known as paraffin (a historical term with several meanings). An alkane is made up of hydrogen and carbon atoms that are organised in a tree structure with single carbon-carbon bonds.  The chemical formula of alkanes is CnH2n+2. The alkanes range in complexity from the simplest example of methane (CH4) (often referred to as the parent molecule) to arbitrarily massive and complicated compounds like pentacontane (C50H102) or 6-ethyl-2-methyl-5-(1-methyl ethyl) octane, an isomer of tetradecane (C14H30).

In an alkane, each carbon atom is sp3-hybridized by four sigma bonds (C–C or C–H), and each hydrogen atom is attached to one of the carbon atoms (in a C–H bond). The carbon skeleton, also known as the carbon backbone, is a molecule’s longest chain of interconnected carbon atoms. The amount of carbon atoms in an alkane can be used to determine its size.

Petroleum (crude oil) and natural gas are the two primary commercial sources of alkanes.

Structure of Alkanes

CnH2n+2 is the general formula for alkanes. An alkane containing 2 (n) carbon atoms, for example, will have 6 (2n + 2) hydrogen atoms. Sigma bonds unite their neighbouring atoms, forming tetrahedral centres surrounding the carbon atoms. Because these are all single bonds, all connections are free to rotate. Each hydrogen atom is connected to a carbon atom by four bonds (either C-H or C-C bonds) (H-C bonds). 

Alkanes, commonly known as paraffin, are a kind of hydrocarbon that is entirely hydrogen-saturated. They have a carbon to hydrogen which is connected covalently since they have no double or triple bonds in their carbon skeletons. Alkenes and alkynes, on the other hand, have double and triple bonds and are classified as unsaturated hydrocarbons.

Alkanes’ Nomenclature

Following the hydrocarbon prefixes, alkanes are given the suffix “-ane.” Methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10), pentane, and other gases are included in the series. The prefixes “hex-,” “hept-,” “oct-,” “non-,” and “dec-” are used for carbon chains with 6, 7, 8, 9, and 10 atoms, respectively.

The four bonds generated by carbon in larger molecular weight compounds allow for a variety of carbon

skeleton modifications. Isomers are different types of molecules that have the same chemical formula. The linear, unbranched forms of these alkanes are designated by the prefix “n-,” which stands for “normal.”

Chemical Properties of Alkanes

Alkanes are the organic compounds with the least amount of reactivity. Alkanes are not completely inert. Combustion, which is the reaction with oxygen, and halogenation, which is the reaction with halogens, are two major processes that they go through.

• Combustion

A combustion reaction is a chemical process that occurs when a material reacts with oxygen and produces heat and light. When ignited, alkanes easily undergo combustion processes. When there is enough oxygen to sustain the entire combustion, the products are carbon dioxide and water.

CH4 + 2O2 →CO2 + 2H2O + energy 

2C6H14 + 19O2 → 12CO2 + 14H2O + energy

The exothermic characteristic of alkane combustion processes explains the broad usage of alkanes as fuels. The majority of natural gas used in residential heating is methane.

• Halogenation

When the alkane is halogenated then one or more halogen atoms are replaced by hydrogen atoms, resulting in a hydrocarbon derivative. The following is an example of an alkane halogenation reaction.

The replacement of the single halogen atom for one of the hydrogen atoms in an alkane has a generic equation.

R-H + X2  →R-X + H-X 

• Aromatisation

At high temperatures and in presence of the catalyst, alkanes having six to ten carbon atoms are transformed into the homologous benzene. Aromatization is the term for this process. It occurs when alkanes undergo simultaneous cyclisation and dehydrogenation.

• Reaction With Steam

In the presence of nickel, methane combines with steam at 1273K and decomposes into carbon monoxide and hydrogen gas.

Steam reforming is a well-established industrial technique for producing H2 gas from hydrocarbons, and it is used to produce H2 gas from methane.

• Pyrolysis

Pyrolysis is described as the application of heat to decompose an organic component into smaller pieces in the absence of air. ‘Pyro’ is Greek for ‘fire,’ and ‘lysis’ is Greek for separating.’ Alkane pyrolysis is also known as cracking.

When alkane vapours are pushed over red-hot metal in the absence of air, they decompose into simpler hydrocarbons.

Conclusion

• Any alkane creates energy when it is burned, as illustrated in the graph below:

• More C-H bonds and C-C bonds are found in a longer carbon chain.

• More C=O bonds (as in CO2) and more O-H bonds are produced by a longer carbon chain (as in H2O).

• Breaking C-C and C-H bonds and forming C=O and O-H bonds releases energy in the whole process.

• The more C-C and C-H bonds that are broken, and the more C=O and O-H bonds that are established, the more energy is released.

• Alkanes are saturated hydrocarbons, which means they have no double or triple bonds in their carbon backbones.

• There are a variety of alkane isomers due to the valence configuration of carbon, which are generally classified into linear and branching forms.

• Alkanes are present in natural gas and petroleum and are employed in a variety of industrial applications.