Lab10 - SN2 Reaction of Alkyl Halides Purpose: To...

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SN 2 Reaction of Alkyl Halides Purpose: To understand the mechanisms of SN 1 and SN 2 reactions. Part 1: The reaction with sodium iodide in acetone is a SN 2 reaction because I- is a good nucleophile due to increasing polarizability. Larger halogens have larger, more diffuse, and more polarizable electron clouds. These electron clouds allow for more effective orbital overlap in the SN 2 transition state. The result is a lower transition- state energy and faster nucleophilic substitution. Also, acetone is a polar aprotic solvent, which does not form hydrogen bonds and effect of solvation is diminished. SN 2 reactions works very well with primary halides, less well with secondary halides, and never works with tertiary halides because the reaction is very sensitive to steric effects. Compounds1, 2, 5, and 7 are all primary halides (which undergo SN 2) , yet have different reaction rates due to the leaving group ability. A leaving group ability can be associated with its capacity to accommodate a negative charge. In addition, good leaving groups (LG) are the conjugate bas of strong acids Hence, for the halogens, leaving group ability increases along the series from fluorine to iodine. Compound 1 reacted the fastest because Br is a better LG than Cl. For compound 5,
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This note was uploaded on 07/23/2010 for the course CHEM Chemistry taught by Professor Nitche during the Spring '08 term at University of California, Berkeley.

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Lab10 - SN2 Reaction of Alkyl Halides Purpose: To...

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