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Chapter 14

CHEM 2OB3 Chapter Notes - Chapter 14: Partial Charge, Alkoxy Group, Sodium Borohydride


Department
Chemistry
Course Code
CHEM 2OB3
Professor
Paul Harrison
Chapter
14

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14: Ethers and Epoxides; Thiols and Sulfides
Ethers
1. Side groups to the left and right of the ether
a. Unsymmetrical: two side groups are different
-Ethyl methyl ether
b. Symmetrical: two side groups are the same
-Diethyl ether
2. Chains to the left and right of the ether
a. Name the parent chain and the alkoxy substituent (includes the O atom; attached to Carbon #1)
-Ethoxy pentane (alphabetized)(E)
Structure and Properties
-Ether acts as a H bond acceptor, by interacting with proton in an alcohol (H bond donator)
-Low boiling points
oHave dipole-dipole interactions help elevate boiling point
oHigher the mass (increase London forces) = higher BP
-Solvents for organic reactions
oUnreactive
oLow BP allows for evaporation after reaction is complete
Crown Ethers
A. Can interact with metals with a full or partial positive charge
oEx. Grignard reagents are formed with ethers: Lone pairs on O stabilize Mg’s charge
-Crown Ethers: cyclic polyethers
oMultiple O bond tightly with metal in the center
B. The outside is a hydrocarbon = soluble in organic solvents
oWith crown ethers, compounds like KF would dissolve in benzene so that the K creates a solvent in
the benzene and the F is freed, allowing it to act as a nucleophile  substitution reactions
-The O all face inwards, where they bind to metal cation
oRenders the metal soluble in nonpolar solvent (ex. Benzene)
Preparation of Ethers
Industrial Preparation of Diethyl Ether (via acid-catalyzed dehydration of ethanol)
-SN2 process
-Ethanol is protonated and attacked by another ethanol in SN2; it’s then deprotonated to create a
poduct
-The acid is a catalyst

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Williamson Ether Synthesis
-Alcohol is deprotonated to form alkoxide ion, which acts as a nucleophile in SN2
-Works best when methyl or primary alkyl halides are
used
oSecondary alkyl halides are less efficient:
elimination is favoured ove substittion
oTertiary alkyl halides cannot be used
Alkoxymercuration-Demercuration
-Oxymercuration-demurcuration (addition): alkenes  alcohols
oReagents: Hg(OAc)2, H20 and NaBH4
-Alkoxymercuration-demurcuration: alkenes 
ethers
oReagents: Hg(OAc)2, ROH and NaBH4
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Reactions of Ethers
Acidic Cleavage
-Ether + excess HI or HBr (acidic
cleavage) 2 alkyl halides
-Phenyl ether + excess HI orHBr  (acidic
cleavage) phenol + alkyl halide
-HCl is less effective
Autooxidation
-Ethers + O2 (slow)  (autooxidation)
hydroperoxides
Naming Epoxides (or Oxiranes)
-Oxiranes are the most reactive
because of significant ring strain
-Can have 4 substituted groups
Two Methods:
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