Reactions Involving Free Radicals
Reactions Involving Free Radicals
Feb 23, 2016
Reactions Involving Free Radicals. Free radical reactions involve one electron species, frequently generated by homolysis (shown below). Radical reactions can be divided into three steps: 1) Initiation 2) Propagation 3) Termination. Weaker bonds are more readily cleaved by homolysis. - PowerPoint PPT Presentation
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Reactions Involving Free Radicals
Free radical reactions involve one electron species, frequently generated by homolysis (shown below)
Radical reactions can be divided into three steps:1) Initiation2) Propagation3) Termination
Weaker bonds are more readily cleaved by homolysis
Some bonds can be cleaved by heating
Radical Bromination
Allylic (and benzylic) bromination with NBS (N-Bromosuccinimide)
NBS is regarded as a source of trace amounts of Br2 via the mechanism shown below.
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 kcalSn-Br 132 KcalSn-I 56 kcal
C-S 65 kcalC-Br 68 kcalC-I 51 kcal
The Barton-McCombie Deoxygenation
Mechanism
Radical Reaction with Allyltributylstannane
The Barton Decarboxylation
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