ORGANIC CHEMISTRY LANEY COLLEGE CHEM 12A Version 2.0, 9/1/06Chapter 8 Learning Objectives and Terminology (Wade) Addition of hydrogen halides (HBr, HCl, HI) to alkenes yields alkyl halides and occurs with Markovnikovselectivity – the halide ends up on the most substituted carbon. Radical addition of HBr (only) gives anti-Markovnikovffaddition (peroxide effect) to alkenes due to a change in the mechanism, which involves the addition of a bromine radical. Addition of X2in halogenated solvents, such as CH2Cl2or CHCl3, proceeds with antiaddition to give 1,2-dihalides (vicinal). Addition of Br2or Cl2in 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 Br2or Cl2also 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 antiaddition products.
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