Chap04 - Reactions of Alkenes Reactions Chapter 4 Chapter...

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Chapter 4 1 Reactions of Alkenes. Reactions of Alkenes. Chapter 4 Chapter 4
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Chapter 4 2 Contents of Chapter 4 Electrophilic Addition Reactions Electrophilic Addition Reactions Carbocations Carbocations Various Addition Reactions Various Addition Reactions
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Chapter 4 3 Mechanism for Electrophilic Addition to Alkenes Reaction of 2-butene with hydrogen bromide is typical of electrophilic addition to alkenes The reaction starts with the slow addition of an electrophile to an sp 2 carbon, resulting in formation of a carbocation The next step is the rapid addition of a nucleophile to the other sp 2 carbon
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Chapter 4 4 Addition of Hydrogen Halides to Alkenes The more substituted carbocation is preferred
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Chapter 4 5 Stability of Carbocations Alkyl groups (“R”s) tend to stabilize the positive charge on the sp 2 carbon of a carbocation
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Chapter 4 6 Structure of the Transition State The product of electrophilic addition to asymmetric alkenes is determined by how fast the various carbocations are formed The lower the G , the faster the reaction Substituents on an sp 2 carbon reduce the free energy of a species Hence if the transition state is similar to the resultant carbocation, it too should be stabilized by alkyl substituents
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This note was uploaded on 12/30/2011 for the course CHEM 2261 taught by Professor Crowe during the Fall '08 term at LSU.

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Chap04 - Reactions of Alkenes Reactions Chapter 4 Chapter...

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