Chapter07b - ± Radical from intiation adds to alkene to...

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1 1 7.9 Biological Alkene Addition Reactions ± Living organisms convert organic molecules using enzymes as catalysts ± Many reactions are similar to organic chemistry conversions, except they occur in neutral water ± Usually much specific for reactant and stereochemistry 2 Biological Hydration Example ± Fumarate to malate catalyzed by fumarase ± Specific for trans isomer ± Addition of H, OH is anti 3 7.10 Addition of Radicals to Alkenes: Polymers ± A polymer is a very large molecule consisting of repeating units of simpler molecules, formed by polymerization ± Alkenes react with radical catalysts to undergo radical polymerization ± Ethylene is polymerized to poyethylene, for example 4 Free Radical Polymerization of Alkenes ± Alkenes combine many times to give polymer ± Reactivity induced by formation of free radicals
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2 5 Free Radical Polymerization: Initiation ± Initiation - a few radicals are generated by the reaction of a molecule that readily forms radicals from a nonradical molecule ± A bond is broken homolytically 6 Polymerization: Propagation
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Unformatted text preview: ± Radical from intiation adds to alkene to generate alkene derived radical ± This radical adds to another alkene, and so on many times 7 Polymerization: Termination ± Chain propagation ends when two radical chains combine ± Not controlled specifically but affected by reactivity and concentration 8 Other Polymers ± Other alkenes give other common polymers 3 9 Unsymmetrical Monomers ± If alkene is unsymmetrical, reaction is via more highly substituted radical 10 Chain Branching During Polymerization ± During radical propagation chain can develop forks leading to branching ± One mechanism of branching is short chain branching in which an internal hydrogen is abstracted 11 Long Chain Branching ± In long chains, a hydrogen from another chain is abstracted 12 Cationic Polymerization ± Vinyl monomers react with Brønsted or Lewis acid to produce a reactive carbocation that adds to alkenes and propagates via lengthening carbocations...
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This note was uploaded on 04/18/2011 for the course CHM 151 taught by Professor Dong during the Winter '08 term at University of Toronto.

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Chapter07b - ± Radical from intiation adds to alkene to...

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