Bromination of alkanes

Initiation

-Bromine molecule is broken by homolytic fission using UV, as the covalent bond is a shared pair of electrons bromine atoms form radicals with an unpaired electron
Br₂→2Br∙

Propagation

-The reaction propagates through two propagation steps
1) CH₄+Br∙→CH₃+HBr
2) CH₃∙+Br₂→CH₃Br+Br∙

Termination

-In this stage two radicals collide, forming a molecule with all electrons paired
1) Br∙+Br∙→Br₂
2) CH₃∙+CH₃∙→C₂H₆
3)CH₃∙+Br∙→CH₃Br

Limitations

-Further substitution: further bromine radicals can collide with the CH₃Br to substitute another hydrogen atom. This can continue till all hydrogen atoms have been substituted
-Substitution at different positions in a carbon chain: with longer carbon chains than methane the Br can substitute anywhere along the carbon chain producing different isomers