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Reaction Mechanism
The reaction mechanisms of alkanes, primarily involve free radical substitution reactions because alkanes are relatively unreactive due to the presence of only single carbon-carbon and carbon-hydrogen bonds.
Methane
Methane is relatively unreactive under standard conditions.
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It can undergo combustion reactions, where it reacts with oxygen to produce carbon dioxide and water.
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The combustion of methane is highly exothermic and releases a significant amount of energy.
Ethane
Ethane can also undergo combustion reactions similarly to methane.
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It can also be halogenated, where it reacts with halogens (e.g., Cl2 or Br2) in the presence of heat or UV light, resulting in the replacement of one or more hydrogen atoms with halogen atoms.
These reactions typically proceed through free radical mechanisms.
Propane
Propane behaves similarly to methane and ethane in combustion reactions and halogenation reactions.
Butane
Butane can participate in combustion and halogenation reactions, typically with chlorine or bromine.
These reactions also follow free radical mechanisms.
Pentane
Pentane and higher alkanes can undergo similar combustion and halogenation reactions as mentioned for smaller alkanes.
They are more complex due to the larger number of hydrogen atoms and the potential for multiple substitution sites.
Hexane to Decane
These alkanes follow the same general principles of combustion and halogenation reactions.
The reactions become progressively more complex as the size of the alkane increases because there are more possible sites for substitution.
In all these reactions, the initiation step involves the generation of free radicals. These free radicals are highly reactive species with unpaired electrons and can initiate a chain reaction of radical reactions.
The propagation steps involve the reactions of free radicals with the alkane, leading to the replacement of hydrogen atoms with halogens or other functional groups.
Alkanes do not easily undergo addition reactions because their carbon-carbon sigma bonds are relatively strong. They can, however, serve as feedstock for various industrial processes, such as the production of alkenes via dehydrogenation or the cracking of longer-chain alkanes to produce smaller alkanes and alkenes.
These processes typically involve high temperatures and catalysts.