Chapter_8_(Wade)

Chapter_8_(Wade) - ORGANIC CHEMISTRY CHEM 12A LANEY COLLEGE...

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ORGANIC CHEMISTRY LANEY COLLEGE CHEM 12A Version 2.0, 9/1/06 Chapter 8 Learning Objectives and Terminology (Wade) Addition of hydrogen halides (HBr, HCl, HI) to alkenes yields alkyl halides and occurs with Markovnikov selectivity – the halide ends up on the most substituted carbon. Radical addition of HBr (only) gives anti- Markovnikovff addition (peroxide effect) to alkenes due to a change in the mechanism, which involves the addition of a bromine radical. Addition of X 2 in halogenated solvents, such as CH 2 Cl 2 or CHCl 3 , proceeds with anti addition to give 1,2- dihalides ( vicinal ). Addition of Br 2 or Cl 2 in water gives halohydrins (addition of HOX). Use of an alcohol instead of water as the solvent give halo ethers. Any addition reaction that involves addition Br 2 or Cl 2 also involves an intermediate bromonium or chloronium ion. Subsequent additions of nucleophiles to this ion occur from the “back” side and gives rise to the observed anti addition products. Alkenes can undergo addition of H
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