1057_RG_9_08 - Chem 1057 J Walcott LEARNING STRATEGIES CENTER Fall 2008 Review Guide#9 Lectures Chapters 8 and 9 II Reactions of Alkyl Halides A

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Chem 1057 J. Walcott LEARNING STRATEGIES CENTER Fall 2008 Review Guide #9 Lectures: 10/27/08 – 10/31/08 : Chapters 8 and 9 II. Reactions of Alkyl Halides A. The S N 2 Reaction 1. The nucleophile replaces the leaving group in a concerted, one-step mechanism (backside attack) that always occurs with inversion. S N 2 reactions will occur with methyl, primary and secondary alkyl halides but not tertiary ones. 2. The S N 2 reaction is overall second order (rate depends on the concentration of both the nucleophile and the substrate). It is a bimolecular reaction (both the nucleophile and the substrate are involved in formation of the rate-determining transition state). 3. S N 2 reactions give complete stereochemical control and will produce one product from a single reactant. 4. The rate of the S N 2 reaction is affected by nucleophilicity and leaving group ability. a. Nucleophilicity correlates roughly with Bronsted basicity. b. The best leaving groups are the weakest bases. 5. The solvent effect is important. a. In aprotic solvents, a nucleophile does not become well solvated or stabilized and is therefore more reactive. b. In a protic solvent, solvation of anions is a very important consideration. A protic solvent stabilizes an anion through formation of hydrogen bonds. The stronger the stabilizing interaction between an anion and the solvent is, the less reactive (and less
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This note was uploaded on 12/17/2008 for the course CHEM 3570 taught by Professor Ganem, b during the Fall '06 term at Cornell University (Engineering School).

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1057_RG_9_08 - Chem 1057 J Walcott LEARNING STRATEGIES CENTER Fall 2008 Review Guide#9 Lectures Chapters 8 and 9 II Reactions of Alkyl Halides A

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