CH06 Instructor Notes

CH06 Instructor Notes - Chapter 6 Reactions of Alkenes...

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Ch221 Chapter 6 Lecture Notes Page 1 of 9 Chapter 6 — Reactions of Alkenes: Addition Reactions I. GENERAL REACTION AB CC + ACCB • C=C π -bond acts as a nucleophile or Lewis base and "attacks" electron deficient species π -Bond acts as a source of electrons for formation of a σ -bond to a new atom II. HYDROGENATION A. Addition of H 2 across C=C • Reaction is exothermic, but requires a catalyst, e.g. platinum H 2 , Pt H 2 , Pt B. Mechanism takes place on a metal surface (heterogeneous catalysis) Carey, Mechanism 6.1 -- PPT C. Stereochemistry of hydrogenation H 2 , Pt CH 3 CH 3 H H 100% cis -1,2-dimethyl cyclohexane • Hydrogenation is stereoselective : single starting material yields a single stereoisomer • Hydrogen adds to the same face of C=C: syn addition • Contrast with anti addition Addition to opposite faces anti addition does not occur CH 3 H CH 3 H
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Ch221 Chapter 6 Lecture Notes Page 2 of 9 • Addition is not only syn, but favors the less hindered face of the C=C H 3 C H 3 C CH 3 H 2 , Ni H H H NOT H Carey, Figure 6.2 --PPT III. ADDITION OF HX Two ways to do this with opposite regiochemistry A. Ionic Mechanism 1. Generally: HBr,CHC l 3 -30 °C Br 76 % 2. Reaction is regioselective: Markovnikov's Rule: H adds to the C with more H substituents, X adds to C with more R substituents HBr Br HCl Cl HBr Br 3. Mechanism — only one of the two possibilities shown below will happen.
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This note was uploaded on 11/13/2010 for the course CH 221 taught by Professor Melander during the Fall '07 term at N.C. State.

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CH06 Instructor Notes - Chapter 6 Reactions of Alkenes...

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