Free Radical Halogenation Of Alkanes

Question

When methane is treated with chlorine in the presence of diffused sunlight, which species is primarily responsible for propagating the chain during the substitution reaction?

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Chlorination of methane proceeds by a free radical substitution mechanism that has three distinct phases: initiation, propagation, and termination. In initiation, $Cl_2$ undergoes homolytic fission under UV light to generate two chlorine radicals, $Cl_2 \rightarrow 2Cl^{\bullet}$. The propagation steps are the heart of the chain: a chlorine radical abstracts a hydrogen atom from methane to give $CH_3^{\bullet}$ and $HCl$, and the methyl radical then reacts with another $Cl_2$ molecule to give $CH_3Cl$ and regenerate $Cl^{\bullet}$. Because $Cl^{\bullet}$ is consumed and regenerated, it is the species that carries the chain forward. The chloride ion $Cl^{-}$ would be involved in ionic, not radical, chemistry, so it is wrong. The chloronium ion $Cl^{+}$ appears in electrophilic addition to alkenes, not in alkane substitution, so it is incorrect. Molecular $Cl_2$ is the reagent but does not itself propagate the chain; it only supplies radicals after homolysis. This mirrors the NCERT treatment of substitution reactions of alkanes. A consistency check: only a radical mechanism explains why traces of light or peroxide dramatically accelerate the reaction.

Free Radical Halogenation Of Alkanes

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Free Radical Halogenation Of Alkanes

Select the correct option:

🔒 Solution Hidden from View

More hydrocarbons Practice Questions

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About This Question

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A hydrocarbon with the molecular formula $C_{6} H_{10}$ is being analysed, and the total number of degr...