1. Reactions Involving Free Radicals

2. Free radical reactions involve one electron species, frequently generated by homolysis (shown below)

4. Radical reactions can be divided into three steps: 1) Initiation 2) Propagation 3) Termination

5. Weaker bonds are more readily cleaved by homolysis

6. Some bonds can be cleaved by heating

7. Radical Initiators AIBN Benzoyl Peroxide Link

10. Radical Bromination

11. Link

13. Allylic (and benzylic) bromination with NBS (N-Bromosuccinimide)

14. NBS is regarded as a source of trace amounts of Br 2 via the mechanism shown below.

17. Reductions utilizing tributyltin hydride as a hydrogen atom donor The Sn-H bond is relatively weak (82 kcal/mole), relative to the C-H bond (99 kcal/mole) By contrast, tin forms stronger bonds to bromine, iodine, and sulfur than does carbon. Sn-S 111 kcal Sn-Br132 Kcal Sn-I56 kcal C-S65 kcal C-Br68 kcal C-I51 kcal

20. The Barton-McCombie Deoxygenation

21. Mechanism

25. Radical Reaction with Allyltributylstannane

27. The Barton Decarboxylation

31. Free Radical Polymerization Link