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CHE 242 Unit V Structure and Reactions of Alcohols, Ethers and Epoxides; Basic Principles of NMR Spectroscopy CHAPTER FOURTEEN Terrence P. Sherlock Burlington County College 2004 Boiling Points Similar to alkanes of comparable molecular weight. Chapter 14 2 Hydrogen Bond Acceptor • Ethers cannot H-bond to each other. • In the presence of -OH or -NH (donor), the lone pair of electrons from ether forms a hydrogen bond with the -OH or -NH. Chapter 14 3 => Solvent Properties • Nonpolar solutes dissolve better in ether than in alcohol. • Ether has large dipole moment, so polar solutes also dissolve. • Ethers solvate cations. • Ethers do not react with strong bases. Chapter 14 => 4 Ether Complexes • Grignard reagents • Electrophiles H _ + O B H H BH3 THF • Crown ethers => Chapter 14 5 Common Names of Ethers • • • • • Alkyl alkyl ether Current rule: alphabetical order Old rule: order of increasing complexity Symmetrical: use dialkyl, or just alkyl. CH3 Examples: CH3CH2 CH3 O CH2CH3 O C CH3 CH3 diethyl ether or ethyl ether Chapter 14 t-butyl methyl ether or methyl t-butyl ether 6 => IUPAC Names • Alkoxy alkane • Examples: CH3 CH3 O CH3 O C CH3 CH3 2-methyl-2-methoxypropane Methoxycyclohexane => Chapter 14 7 Naming Epoxides • Alkene oxide, from usual synthesis method H peroxybenzoic acid O cyclohexene oxide H • Epoxy attachment to parent compound, 1,2-epoxy-cyclohexane • Oxirane as parent, oxygen number 1 H CH3CH2 O CH3 H trans-2-ethyl-3-methyloxirane Chapter 14 => 8 Spectroscopy of Ethers • IR: Compound contains oxygen, but O-H and C=O stretches are absent. • MS: -cleavage to form oxonium ion, or loss of either alkyl group. • NMR: 13C-O signal between 65-90, 1H-C-O signal between 3.5-4. => Chapter 14 9 Williamson Synthesis • Alkoxide ion + 1 alkyl bromide (or tosylate) • Example: CH3 CH3 O H + K CH3 CH3 CH3 CH3 _ O + CH3CH2 CH3 CH3 H C CH3 _ + O K CH3 Br CH3 H _ O CH2CH2CH3 + Br CH3 Chapter 14 => 10 Phenyl Ethers • Phenoxide ions are easily produced for use in the Williamson synthesis. • Phenyl halides or tosylates cannot be used in this synthesis method. _ O Na+ O H + NaOH + HOH => Chapter 14 11 Bimolecular Dehydration of Alcohols • Industrial method, not good lab synthesis. • If temperature is too high, alkene forms. CH3CH2 O H + H O CH2CH3 H2SO4 CH3CH2 O CH2CH3 140°C => Chapter 14 12 Cleavage of Ethers • Ethers are unreactive toward base, but protonated ethers can undergo substitution reactions with strong acids. • Alcohol leaving group is replaced by a halide. • Reactivity: HI > HBr >> HCl => Chapter 14 13 Mechanism for Cleavage • Ether is protonated. CH3 O CH3 H Br CH3 H + O CH3 _ _ + Br • Alcohol leaves as halide attacks. _ Br CH3 H + O CH3 Br CH3 + H O CH3 • Alcohol is protonated, halide attacks, and another molecule of alkyl bromide is formed. => Chapter 14 14 Phenyl Ether Cleavage • Phenol cannot react further to become halide. • Example: OH O CH2CH3 HBr Chapter 14 + CH3CH2 Br => 15 Autoxidation of Ethers • In the presence of atmospheric oxygen, ethers slowly oxidize to hydroperoxides and dialkyl peroxides. • Both are highly explosive. • Precautions: Do not distill to dryness. Store in full bottles with tight caps. => Chapter 14 16 POWER POINT IMAGES FROM “ORGANIC CHEMISTRY, 5TH EDITION” L.G. WADE ALL MATERIALS USED WITH PERMISSION OF AUTHOR PRESENTATION ADAPTED FOR BURLINGTON COUNTY COLLEGE ORGANIC CHEMISTRY COURSE BY: ANNALICIA POEHLER STEFANIE LAYMAN CALY MARTIN Chapter 14 17