Transcript Chapter 14 - Chemistry Solutions

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