Expalain the free radical substitution of alkane?

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Expalain the free radical substitution of alkane?

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Answer 1 · 2018-03-26T18:28:05

See below:

Explanation:

Alkanes can be converted to Halogenalkanes through a free radical substitution as free radicals are highly reactive.

This is best broken down into 3 steps: Initiation, Propagation and Termination

Lets use the reaction between Chlorine and Methane ( $C H_{4}$ $CH_4$ ), which can occur in the atmosphere.

Initation

$C l_{2} \to 2 C l^{.}$ $Cl_2 -> 2Cl^.$ A chlorine molecules is broken down by UV light and undergoes homolytic fission (electrons in the split covalent bond goes to each of the two atoms, which turn into free radicals- a species with an unpaired electron= reactive.)
Propagation
These free radicals will go on and react with other molecules around them: like Methane.

$C l^{.} + C H_{4} \to H C l + C H_{3}^{.}$ $Cl^.+CH_4 -> HCl + CH_3^.$

The free radical will donate it's lone electron to form a new covalent bond with Hydrogen, causing the C-H bond in Methane to split and creating a new radical (a methyl radical) which will go on reacting.

$C H 3^{.} + C l_{2} \to C H 3 C l + C l^{.}$ $CH3^.+Cl_2 -> CH3Cl + Cl^.$

This step can form the halogenalkane, chloromethane.

3 Termination
When two radicals react together to from a new molecule which will not go on reacting. This can also form the desired product.

$C H 3^{.} + C l^{.} \to C H 3 C l$ $CH3^. + Cl^. ->CH3Cl$

This also produced Chloromethane.

Or form a new alkane in this case:

$C H 3^{.} + C H 3^{.} \to C_{2} H_{6}$ $CH3^. + CH3^. -> C_2H_6$

Which produces Ethane.

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Expalain the free radical substitution of alkane?

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