057_Ho_13_RG_10_07 - Chem 057 J. Walcott CENTER FOR...

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Chem 057 CENTER FOR LEARNING AND TEACHING Handout #13 J. Walcott LEARNING STRATEGIES CENTER Fall 2007 Review Guide #10 Lectures: 10/29/07 – 11/2/07: Chapter 10 I. The E2 Reaction A. The E2 reaction is a single-step, concerted mechanism consistent with the overall second order kinetics and a bimolecular rate-determining step. B. The regioselectivity of this reaction is determined by Zaitzeff's rule, which says that the most stable alkene product is the major product (thermodynamically favored). Recall that alkene stability increases with branching at the double bond carbon atoms. As a consequence, the major elimination product tends to be the most highly branched alkene. C. syn coplanar elimination and anti coplanar elimination occurs because of the way the orbitals must overlap in forming the new pi bond. coplanar is generally favored because of the preferred reactant conformation. However, steric factors must be considered when determining how the reaction proceeds (whether or coplanar) and what the products will be. D. Factors affecting the rate of E2, and the competition between E2 and S N 2: 1. Better leaving group ability increases the rate of E2, but also increases the rate of S N 2, since in both cases the leaving group leaves in the rate-determining step of the reaction. 2. The branching on secondary and tertiary carbons and branching tends to favor E2 over S N 2 (3 ° > 2 ° > 1 ° ). Similarly, a high degree of branching in the attacking base
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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 University (Engineering School).

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057_Ho_13_RG_10_07 - Chem 057 J. Walcott CENTER FOR...

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