# Expalain the free radical substitution of alkane?

Mar 26, 2018

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 ($C {H}_{4}$), which can occur in the atmosphere.

Initation

1. $C {l}_{2} \to 2 C {l}^{.}$ 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.)

2. Propagation
These free radicals will go on and react with other molecules around them: like Methane.

$C {l}^{.} + C {H}_{4} \to H C l + C {H}_{3}^{.}$

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.

$C H {3}^{.} + C {l}_{2} \to C H 3 C l + C {l}^{.}$

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.

$C H {3}^{.} + C {l}^{.} \to C H 3 C l$

This also produced Chloromethane.

Or form a new alkane in this case:

$C H {3}^{.} + C H {3}^{.} \to {C}_{2} {H}_{6}$

Which produces Ethane.