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057_Ho_14_RG_11_07 - Chem 057 J Walcott CENTER FOR LEARNING...

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Chem 057 CENTER FOR LEARNING AND TEACHING Handout #14 J. Walcott LEARNING STRATEGIES CENTER Fall 2007 Review Guide #11 Lectures: 11/5/07 – 11/9/07: Chapter 10 I. Alcohols A. Nomenclature You should understand the nomenclature rules discussed in class. The group priorities so far are alcohols > alkene > alkynes > halogens, ethers and alkyl groups. B. Synthesis of Alcohols and Alcohol Derivatives 1. From Alkenes: The methods for synthesis of alcohols from alkenes that we have examined so far include: hydroboration-oxidation, oxymercuration-reduction, acid catalyzed hydration and treatment of the alkene with osmium tetroxide to produce a glycol or diol. 2. From Alkyl Halides: An S N 2 reaction of an alkyl halide with NaOH or anS N 1 reaction with water and heat can also produce alcohols. 3. Grignard reagent (next page) C. Reactions of Alcohols 1. Acid-catalyzed dehydration : This reaction is simply the reverse of acid-catalyzed hydration of an alkene. You already know the mechanism (E1). Note that protonation of the alcohol oxygen serves to weaken the carbon-oxygen bond and to convert the –OH into a better leaving group. The acid catalyst is regenerated when water removes an ± -H to produce the alkene. Zaitsev regiochemistry is observed, and rearrangement products are possible due to involvement of a carbocation intermediate. Since this is an equilibrium reaction, alkene formation is favored when water is removed and alcohol formation is favored when excess water is present. An alcohol is not a good substrate for E2 reactions because the –OH hydrogen is slightly acidic and the strong base required for an E2 reaction can react with the –OH hydrogen instead of removing the ± -H. 2. Conversion to alkyl halides: Alcohols can react with hydrogen halides via S N 1 or S n 2 reactions to make alkyl halides. Professor Ruttledge demonstrated some reactions where alcohols are converted to alkyl halides more reliably.
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