057_Ho_12_RG_9_07 - Chem 057 J. Walcott CENTER FOR LEARNING...

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Chem 057 CENTER FOR LEARNING AND TEACHING Handout #12 J. Walcott LEARNING STRATEGIES CENTER Fall 2007 Review Guide #9 Lectures: 10/22/07 – 10/26/07 : Chapters 7 and 8 I. The Diels Alder Reaction (continued from Review Guide #7) Conjugated dienes undergo cycloaddtion reactions with dienophiles to give cyclic products. The four carbon atoms of the diene and two carbon atoms of the dienophile combine to form a six- membered ring. Two sigma bonds are formed and there are two fewer pi bonds in the product than in the reactants. The diene must be able to assume an s-cis conformation. Most commonaly, the dienophile is electron deficient and the diene is electron rich. The Diels Alder reaction is a pericycle reaction – a reaction that takes place in a single step, without intermediates, and involves a cyclic redistribution of bonding electrons. A. It is one of the simplest reactions that can be used to form six-membered rings. B. It is one of the few reactions that can be used to form two new carbon-carbon bonds at the same time C. It is stereospecific and regioselective. 1. The reaction is stereospecific at the dienophile. If the dienophile is a cis isomer, then the substituents cis to each other in the dienophile are cis in the product. If the dienophile is a trans isomer, substituents that are trans in the dienophile are trans in the product. 2. The reaction is stereospecific at the diene. Groups on the 1 and 4 position of the diene retain their relative orientation. 4. The endo product is generally favored when either the diene or the dienophile is cyclic. The outcome is less predictable (ie. a mix of endo and exo products) when either of them
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057_Ho_12_RG_9_07 - Chem 057 J. Walcott CENTER FOR LEARNING...

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