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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 Chapter 14 17 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 18