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CHEM 2332H
Christopher J.Douglas

Chapter 14 Book Notes Ethers, Epoxides, and Thioethers 14.1: Introduction • Ethers: compounds of formula R—O—R’ o R and R’can be alkyl or aryl (benzene rings) groups o ethers related to water (like alcohols) w/ alkyl groups replacing H; in alcohol, 1 H replaced, in ether, both H’s replaced o symmetrical ether: 2 alkyl groups = same o unsymmetrical ether: 2 alkyl groups = different • Ethers other than epoxides = relatively unreactive not frequently used as synthetic intermediates o stable w/ many types of reagents used as solvents for organic rxns • Diethyl ether (aka ethyl ether or ether) = most important commercial ether o good solvent for rxns and extractions o used as volatile starting fluid for diesel and gasoline engines o surgical anesthetic for over 100 yr (starting 1842) but highly flammable patients often vomited as they regained consciousness  now use less flammable, more easily tolerated compounds like nitrous oxide (N O) and halothane (CF —CHClBr) 2 3 14.2: Physical Properties of Ethers • 14.2A) Structure and Polarity of Ethers o bent structure, sp hybrid O nearly tetrahydral bond angle like water o in water, nonbonding electrons compress bond angle to 104.5 o typical ether, alkyl groups bulk enlarges bond angle dimethyl ether has angle of 110 o strongly polar even though don’t have hydroxyl groups of alcohols can be good polar solvent w/o reactivity like hydroxyl group • 14.2B) Boiling Points of Ethers; Hydrogen Bonding o Ethers don’t do hydrogen bonding like alcohols b/c no OH groups lower boiling points o But still have big enough dipole moments for dipole-dipole interactions, but relatively little effects on boiling points o Can do hydrogen bonding with other compounds w/ OH or NH groups even though ethers themselves don’t have that group  H bonding needs H bond donor and H bond acceptor  donor = molecule w/ OH or NH group  acceptor = molecule whose lone electron pairs form weak partial bond to H from donor; ether has lone pair on O  ethers can’t H bond w/ other ether molecules  = more volatile than similar-weighted alcohols • 14.2C) Ethers as Polar Solvents o Ethers dissolve variety of polar/nonpolar substances  relatively low boiling points can be evaporated from rxn products  nonpolar substances more soluble in ethers than alcohols b/c ethers don’t have H bonding network to be broken up by nonpolar solute o Polar substances almost as soluble in ethers as alcohols b/c ethers have large dipole moments & can = H bond acceptors  cations effectively solvated by nonbonding electron pairs in ether  anions not as effectively solvated as in alcohols, esp. small, hard anions (ex: fluorides) b/c need strong solvation to overcome ionic bonding, which needs strong H bond donors (ether’s aren’t donors)  but large, diffuse anions (ex: iodides
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