1. Ethers

2. Structure
The functional group of an ether is an oxygen atom bonded to two carbon atoms
in dialkyl ethers, oxygen is sp3 hybridized with bond angles of approximately 109.5°.
in dimethyl ether, the C-O-C bond angle is 110.3°

3. Structure
in other ethers, the ether oxygen is bonded to an sp2 hybridized carbon
in ethyl vinyl ether, for example, the ether oxygen is bonded to one sp3 hybridized carbon and one sp2 hybridized carbon

4. Nomenclature: ethers IUPAC: the longest carbon chain is the parent
name the OR group as an alkoxy substituent
Common names: name the groups bonded to oxygen in alphabetical order followed by the word ether O H C H 3 C H 3 O C H 3 2 O O C H 2 3 C H 3
Ethoxyethane
(Diethyl ether)
trans-
2-Ethoxy-
cyclohexanol
2-Methoxy-2-
methylpropane (
tert-
Butyl methyl ether)

5. Nomenclature: ethers
Although cyclic ethers have IUPAC names, their common names are more widely used
IUPAC: prefix ox- shows oxygen in the ring
the suffixes -irane, -etane, -olane, and -ane show three, four, five, and six atoms in a saturated ring

6. Physical Properties
Although ethers are polar compounds, only weak dipole-dipole attractive forces exist between their molecules in the pure liquid state

7. Physical Properties Boiling points of ethers are
lower than alcohols of comparable MW
close to those of hydrocarbons of comparable MW
Ethers are hydrogen bond acceptors
they are more soluble in H2O than are hydrocarbons

8. Preparation of Ethers
Williamson ether synthesis: SN2 displacement of halide, tosylate, or mesylate by alkoxide ion

9. Preparation of Ethers yields are highest with methyl and 1° halides,
lower with 2° halides (competing -elimination)
reaction fails with 3° halides (-elimination only)

10. Preparation of Ethers Acid-catalyzed dehydration of alcohols
diethyl ether and several other ethers are made on an industrial scale this way
a specific example of an SN2 reaction in which a poor leaving group (OH-) is converted to a better one (H2O)

11. Preparation of Ethers Step 1: proton transfer gives an oxonium ion
Step 2: nucleophilic displacement of H2O by the OH group of the alcohol gives a new oxonium ion

12. Preparation of Ethers
Step 3: proton transfer to solvent completes the reaction

13. Preparation of Ethers Acid-catalyzed addition of alcohols to alkenes
yields are highest using an alkene that can form a stable carbocation
and using methanol or a 1° alcohol that is not prone to undergo acid-catalyzed dehydration

14. Preparation of Ethers
Step 1: protonation of the alkene gives a carbocation
Step 2: reaction of the carbocation (an electrophile) with the alcohol (a nucleophile) gives an oxonium ion

15. Preparation of Ethers
Step 3: proton transfer to solvent completes the reaction

16. Cleavage of Ethers
Ethers are cleaved by HX to an alcohol and a haloalkane
cleavage requires both a strong acid and a good nucleophile; therefore, the use of concentrated HI (57%) and HBr (48%)
cleavage by concentrated HCl (38%) is less effective, primarily because Cl- is a weaker nucleophile in water than either I- or Br-

17. Cleavage of Ethers
A dialkyl ether is cleaved to two moles of haloalkane

18. Cleavage of Ethers
Step 1: proton transfer to the oxygen atom of the ether gives an oxonium ion
Step 2: nucleophilic displacement on the 1° carbon gives a haloalkane and an alcohol
the alcohol is then converted to an haloalkane by another SN2 reaction

19. Cleavage of Ethers
3°, allylic, and benzylic ethers are particularly sensitive to cleavage by HX
tert-butyl ethers are cleaved by HCl at room temp
in this case, protonation of the ether oxygen is followed by C-O cleavage to give the tert-butyl cation

20. Oxidation of Ethers
Ethers react with O2 at a C-H bond adjacent to the ether oxygen to give hydroperoxides
reaction occurs by a radical chain mechanism
Hydroperoxide: a compound containing the OOH group