Answer to Question #111248 in Organic Chemistry for Zainah

Question

Describe how homolytic fission leads to the mechanism of radical substitution in alkanes.

Answer 1

Let's have a look at the mechanism of methane halogenation:

1 step - homolytic fission under the action of light or high temperature with generation of free radicals:

Cl₂ = Cl• + Cl•

A radical is a particle that contains an indivisible pair of valence electrons. It's high reactive form of atom with high energy, that's way it can react with stable moleculas (such as methane) with substitution of CH₃•.

2 step - chain growth:

CH₄ + Cl• = HCl + CH₃•

CH₃• + Cl₂ = CH₃Cl + Cl•

Such chain reaction may continue with the formation of more chlorine-substituted forms of methane, ethane, etc.

3 step - recombination of the radicals:

Cl• + Cl• = Cl₂

Cl• + CH₃• = CH₃Cl

CH₃• + CH₃• = C₂H₆

Have a great day and be healthy!