057_Ho_15_RG_12_07

057_Ho_15_RG_12_07 - Chem 057 J Walcott CENTER FOR LEARNING...

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Chem 057 CENTER FOR LEARNING AND TEACHING Handout #15 J. Walcott LEARNING STRATEGIES CENTER Fall 2007 Review Guide #12 Lectures: 11/12/07 – 11/16/07: Chapters 11 and 12 I. Free Radical Reactions A. Free-radical addition of HBr to an alkene. The presence of peroxides leads to addition of HBr to an alkene with anti-Markovnikov regiochemistry. The stability order of alkyl free radicals is the same as the stability order of carbocations, for the same reasons. Free radical reaction mechanisms involve movement of single electrons rather than pairs of electrons. Know how to use “fishhook arrows” to represent movement of single electrons in a free-radical reaction mechanism. You should be able to write the mechanism and be able to classify each step as initiation , propagation , or termination . This free radical addition reaction does not occur with HCl or HI. Bond strength between C and I disfavors the propagation step in the case of HI, and the bond strength between H and Cl disfavors the propagation step in the case of HCl. B. Chlorination and Bromination of Alkanes Alkanes react with chlorine or bromine in the presence of light or at high temperatures to form alkyl chlorides or alkyl bromides. The radical halogenation reactions undergo the initiation, propagation and termination steps similar to those in the free-radical reaction of HBr to an alkene. The reaction is
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This note was uploaded on 09/12/2008 for the course CHEM 057 taught by Professor Walcott, j during the Fall '07 term at Cornell.

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057_Ho_15_RG_12_07 - Chem 057 J Walcott CENTER FOR LEARNING...

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