1057-RG_8-09 - Chem 1057 J. Walcott LEARNING STRATEGIES...

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Chem 1057 J. Walcott LEARNING STRATEGIES CENTER Fall 2009 Review Guide #8 Lectures: 10/19/09 – 10/23/09: Chapters 7 and 8 I. The Diels Alder Reaction 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. 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 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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1057-RG_8-09 - Chem 1057 J. Walcott LEARNING STRATEGIES...

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