reaction mechanisms

• 3 stages of radical substitution

  initiation, propagation, termination
• initiation

  molecule is broken by homolytic fission, and each atom takes one electron from the covalent bond, forming two highly reactive radicals.
• initiation example

  Br-Br -> Br$\cdot$ + Br$\cdot$
• propagation step 1 (bromine as example)

  bromine radical reacts with C-H bond in methane, forming a methyl radical and a molecule of hydrogen bromide
• propagation step 2 (bromine as example)

  each methyl radical reacts with another bromine molecule, forming the organic product Bromomethane with another new bromine radical
• propagation step 1 example

  CH4 + Br$\cdot$ -> $\cdot$CH3 + HBr
• propagation step 2 example

  $\cdot$CH3 + Br2 -> CH3Br + Br$\cdot$
• termination step 1 example

  $\cdot$Br +$\cdot$Br $\rightarrow$ Br2
• termination step 2 example

  $\cdot$CH3 + $\cdot$CH3 $\rightarrow$C2H6
• termination step 3 example

  $\cdot$CH3 + $\cdot$Br $\rightarrow$ CH3Br