Chapter 18 - HBr or HI will cleave an ether, may be SN1...

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Sheet1 Page 1 Chapter 18: Ethers and Epoxides 18.1 Names and Properties of Ethers No other functional groups: ether is parent, the two organic substituents are named and listed in alphabetical order Ether as substituent: ether is an alkoxy substituent Same geometry as water: slight dipole moments, relatively unreactive 18.2 Synthesis of Ethers Symmetrical Ethers: Sulfuric acid-catalyzed dehydration of primary alcohols by SN2 mechanism Williamson Synthesis: form an alkoxide ion (use NaH/THF) and react with a primary alkyl halide or tosylate an SN2 reaction occurs and attaches the R group of the alkyl halide to the alcohol Ag2O may be used instead of NaH *alkyl halide must be primary, otherwise E2 reaction will occur instead **should use more hindered alkoxide and less hindered alkyl halide** Alkoxymercuration of Alkenes: alkene + alcohol --(CF3CO2)2Hg--> markovnikov addition of the alcohol and its R group to form an ether 18.3 Reactions of Ethers: Acidic Cleavage
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Unformatted text preview: HBr or HI will cleave an ether, may be SN1 (tertiary) or SN2 (primary or secondary) depending on structure SN2: ether is protonated, halide attacks at less hindered site, giving an alcohol and an alkyl halide SN1: ether is protonated, dissociation occurs to give the more stable carbocation SN1: use HI E1: use CF3CO2H 18.4 Reactions of Ethers: Claisen Rearrangement 18.5 Cyclic Ethers: Epoxides Preparation: alkene --RCOOOH(peroxyacid)--> epoxy + metachlorobenzoic acid (no intermediates) usually, meta-chloroperoxybenzoic acid (M-CPBA) is used Intramolecular Williamson Synthesis: hexene + X2/H2O --> trans-halohydrin --base (NaOH)--> [alkoxide] --> epoxy by SN2 mechanism Sheet1 Page 2 18.6 Reactions of Epoxides: Ring-Opening Acid Catalyzed: SN2, yields a trans-1,2-diol alcohol is protonated, SN2 attack occurs, alcohol is deprotonated, catalyst is reformed Sheet1 Page 3 Thiols and Sulfides Sheet1 Page 4...
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This note was uploaded on 04/26/2009 for the course CHEM 227 taught by Professor Santander during the Fall '08 term at Texas A&M.

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Chapter 18 - HBr or HI will cleave an ether, may be SN1...

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