PSU_Justik_Spring09_Exp1 - Experiment 1 CHEM 213...

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Introduction It is well known that the reaction of molecular bromine (Br 2 ) and water with an alkene yields a bromohydrin via an electrophilic addition mechanism (Chapter 14, Smith). However, molecular bromine is a strong oxidizer and readily generates hydrogen bromide gas. Therefore, less toxic sources of bromine, such as N -bromosuccinimide (NBS), are used when possible. NBS is known to generate low concentrations of Br 2 by the reaction of internally generated HBr (sol.) with NBS (eq. 1). Therefore, the mechanisms for addition reactions involving NBS are essentially the same as those involving Br 2 . A bromonium ion or carbocation is formed, and then the nucleophile adds to the intermediate. In this experiment, the bromohydrin of α -methyl styrene will be prepared by the action of NBS and water in ace- tone (above). Because two non-identical groups are added to the π -bond, two regioisomers (constitutional isomers) are possible for this reaction. The first objective of this experiment is to determine which regioisomer (A or B) is the major product for the reac- tion. Once the identity of the product is determined, the primary objective of the experiment can then be ad- dressed. That is, the supposition of whether the second mechanistic step (Scheme 1) of this electrophilic reaction
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This note was uploaded on 09/29/2010 for the course CHEM 213CCF taught by Professor Staff during the Spring '08 term at Pennsylvania State University, University Park.

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PSU_Justik_Spring09_Exp1 - Experiment 1 CHEM 213...

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