chem lab 6 - Hoang 1 Phuong Hoang Chem 3105 541 10/15/08...

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Hoang 1 Phuong Hoang Chem 3105 – 541 10/15/08 Experiment 6: Bromination of ( E )-Stibene I. Purpose: The purpose of this experiment is to synthesize meso-dibromostibene from stibene. II. Background: The reaction of synthesizing meso-dibromostibene: This reaction is classed as stereospecific because the other possible diastereomers are not formed. The reaction proceeds in two stages. The first step is the formation of an intermediate cyclic bromonium ion. This formation can be explained as the bromine molecule, normally symmetrical, approaches the nucleophilic and electron-rich π bond of alkenes and becomes polarized by induction and can then function as the electrophile in addition reaction. The result is the generation of a cyclic bromonium ion: In the present reaction, both the bromine and ( E )-stibene are achiral but the product is chiral. The generation of the three-membered ring intermediate has a profound effect on the stereochemistry of the second step of the bromine addition. In the second step, the bromide ion attacks on the intermediate bromonium ion. Because
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This note was uploaded on 01/28/2009 for the course CHEM 3105 taught by Professor Zhang during the Spring '09 term at Texas Tech.

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chem lab 6 - Hoang 1 Phuong Hoang Chem 3105 541 10/15/08...

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