A to Z Directory – Virginia Commonwealth University
Chapter 14
• Physical Properties of Ethers
o Fairly low boiling point because there is no hydrogen-bonding in pure ethers.
▪ Ethers can accept hydrogen bonds when in solution with hydrogen-bonding compounds.
o Why ethers make good solvents
▪ Dissolve a wide range of solutes.
• Moderately polar
▪ Fairly nonreactive in a large variety of conditions
▪ Volatile (low-boiling): easily removed by evaporation
▪ Inexpensive
o Crown ethers
▪ Solvate specific cations based on the size of the cavity in the middle.
▪ Ex. [pic]
• Nomenclature of ethers
o Common Names
▪ “alkyl alkyl ether”
• Name each alkyl piece separately, then say “ether”
[pic]
o Ethyl isopropyl ether
• “dialkyl ether” if it’s a symmetrical ether
[pic]
o Diisopropyl ether
o IUPAC
▪ Name the smaller, less complex piece as “alkoxy”
• Ex. –OCH3 would be “methoxy”
▪ The ether has no priority.
[pic]
• 7-ethoxyoct-1-ene
▪ To name epoxides, just say the number of the two carbons attached to the oxygen, followed by “epoxy”
[pic]
▪ 7,8-epoxyoctan-2-ol
• Don’t worry about naming them as “oxiranes.”
• Review of the Synthesis of Ethers
o Williamson Ether Synthesis – See Chapter 11 Notes
▪ Intramolecular Williamson Ether Syntheses
• Chemically, this is not any different, but sometimes it can be difficult to figure out where substituents go on the product.
• To make this easy on yourself, number all the atoms!
[pic]
• Then, make your ring with the correct number of atoms
[pic]
• Now, add your substituents, making sure that they’re connected to the same atoms as before.
[pic]
o Alkoxymercuration-demercuration – See Chapter 8 Notes
o Industrial Synthesis of Symmetrical Ethers – See Chapter 11 Notes
• Cleavage of Ethers of HBr and HI
o HCl doesn’t work because it isn’t acidic enough
o Step 1: Protonation of the oxygen to make a good leaving group (yawn)
[pic]
o Step 2: X- attacks in an SN1 or SN2 mechanism (SN1 is better so if you’re asked to draw a mechanism of this, do the SN1 first if possible)
[pic]
o Step 3: The resulting alcohol further reacts with the HBr or HI to give the corresponding alkyl halide
▪ See Chapter 11 Notes for mechanism
• Autoxidation of ethers
o Once ethers are exposed to oxygen, they can begin to slowly turn into peroxides.
o Peroxides are contact explosives, so if crystals get under the cap of a jar, when you open the jar, it explodes.
o You don’t need to know more than that.
• Sulfur-containing compounds
o You need to be able to draw and identify each of these types of compounds.
o If you just remember the names in this order, it’s easy because you add another oxygen each time.
[pic] [pic] [pic] [pic] [pic]
• Synthesis of epoxides
o Epoxidation of alkenes
▪ See Chapter 8 Notes
o Cyclization of Halohydrins
▪ Formation of halohydrins
• See Chapter 8 Notes
▪ Step 1: Hydroxide deprotonates the hydroxyl group
[pic]
• This should look wrong because we’ve said before that you can’t quantitatively deprotonate alcohols with hydroxide because it isn’t strong enough.
• This action does go to completion, not because the base is so strong, but because the next step is favorable.
o If you use the product of one step as a reagent in a favorable subsequent step, you drive the equilibrium of the first step forward. (LeChatelier just won’t leave us alone!)
o This reaction is what made coupled reactions make sense for me in biology, so maybe those of you who really like biology will find that your understanding of coupled reactions will make this make more sense.
▪ Step 2: The negatively-charged oxygen kicks off the halogen in an intramolecular SN2.
[pic]
• Ring opening of epoxides
o Acid-Catalyzed
▪ The nucleophile hits the more substituted side of the epoxide ring
• This is because the more substituted side has a larger partial positive charge.
[pic]
o Base-Catalyzed
▪ The nucleophile hits the less substituted side of the epoxide ring.
• This is because of steric effects.
• This is true of all bases, not just hydroxide and alkoxides.
o There’s no point in treating Grignards and organolithiums differently here because they’re just bases too!
• You will often see the conjugate acid of the base used as the solvent.
o Don’t freak out!
o Use the strongest nucleophile present (the base)
[pic]
• Epoxy resins
o You don’t need to know anything about these, but they’re delightful (and installing them as flooring in food-processing plants is a noble and glamorous calling).
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