1. TY 2003 Organic Mechanism 3 Reaction of Chlorine with Methane

2. TY 2003 Free Radical Substitution 1.Initiation 1.Initiation – produces free radicals 2.Propagation 2.Propagation – free radicals react with molecules to produce more free radicals 3.Termination 3.Termination – free radicals react to produce molecules Overall equation CH 4 + Cl 2 CH 3 Cl + HCl

3. TY 2003 First Step - Initiation Cl Cl Initiation involves the production of free radicals Cl Cl UV light is required for this step, it provides the energy to split the Cl-Cl bond Homolytic Fission occurs Free Radicals are formed

4. TY 2003 Homolytic Fission a covalent bond breaks so that one electron from the shared pair goes to each atom Free Radical any species with an unpaired electron Initiation – Key Terms

5. TY 2003 Cl 2 2Cl

6. TY 2003 Second Step - Propagation No light is required for this stage All bonds split homolytically Every reaction produces a free radical Propagation involves the reaction of free radicals with molecules to produce free radicals

7. TY 2003 Molecule H Cl + H C H H Free Radical H Cl H + C H H H C + Cl Cl H H C Cl + Cl H

8. TY 2003 Final Step - Termination This final step can involve any two free radicals No light is required for this step Chloromethane is produced but many other products are also formed because there are lots of different free radicals which can combine Termination involves the reaction of free radicals to produce a molecule

9. TY 2003 Cl + Cl H H C H C H H H Cl + C H H Cl C H H Cl Cl H H H C C H H H