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11: Alkenes- Reactions and Synthesis

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    As you have seen, addition reactions dominate the chemistry of alkenes. This chapter shows how a variety of reagents can add to alkenes; how hydrogen bromide can be made to add to alkenes in a non-Markovnikov manner; and how alkene molecules can be cleaved into easily identifiable parts. First, you will examine the preparation of alkenes by elimination reactions.

    • 11.1: Chapter Objectives
    • 11.2: Preparation of Alkenes - A Preview of Elimination Reactions
    • 11.3: Halogenation of Alkenes - Addition of X₂
    • 11.4: Halohydrins from Alkenes - Addition of HOX
      Lewis acids like the halogens, boron hydrides and certain transition metal ions are able to bond to the alkene pi-electrons, and the resulting complexes rearrange or are attacked by nucleophiles to give addition products.The electrophilic character of the halogens is well known. Chlorine (Cl2) and bromine(Br2) react selectively with the double bond of alkenes, and these reactions are what we will focus on. Fluorine adds uncontrollably with alkenes,and the addition of iodine is unfavorable, so th
    • 11.5: Hydration of Alkenes - Addition of H₂O by Oxymercuration
      Electrophilic hydration is the act of adding electrophilic hydrogen from a non-nucleophilic strong acid (a reusable catalyst, examples of which include sulfuric and phosphoric acid) and applying appropriate temperatures to break the alkene's double bond. After a carbocation is formed, water bonds with the carbocation to form a 1º, 2º, or 3º alcohol on the alkane.
    • 11.6: Hydration of Alkenes - Addition of H₂O by Hydroboration
    • 11.7: Reduction of Alkenes - Hydrogenation
      Addition of hydrogen to a carbon-carbon double bond is called hydrogenation. The overall effect of such an addition is the reductive removal of the double bond functional group. Regioselectivity is not an issue, since the same group (a hydrogen atom) is bonded to each of the double bond carbons. The simplest source of two hydrogen atoms is molecular hydrogen, but mixing alkenes with hydrogen does not result in any discernible reaction.
    • 11.8: Oxidation of Alkenes to Vicinal Diols
      Oxacyclopropane rings, also called epoxide rings, are useful reagents that may be opened by further reaction to form anti vicinal diols. One way to synthesize oxacyclopropane rings is through the reaction of an alkene with peroxycarboxylic acid.
    • 11.9: Oxidation of Alkenes - Cleavage to Carbonyl Compounds
      Ozonolysis is a method of oxidatively cleaving alkenes or alkynes using ozone ( O 3 O3 ), a reactive allotrope of oxygen. The process allows for carbon-carbon double or triple bonds to be replaced by double bonds with oxygen. This reaction is often used to identify the structure of unknown alkenes. by breaking them down into smaller, more easily identifiable pieces. Ozonolysis also occurs naturally and would break down repeated units used in rubber and other polymers.

    11: Alkenes- Reactions and Synthesis is shared under a CC BY-SA 4.0 license and was authored, remixed, and/or curated by Steven Farmer & Dietmar Kennepohl.