Transcript lecture 1 - alcohols-ethers

Dr A.K.M. Shafiqul Islam
University Malaysia Perlis
Alcohols and ethers are organic derivatives
of water where one or both H atoms are
replaced by R groups.
H-O-H  R-O-H  R-O-R’
Alcohol
Ether
Water
Alcohols
• Functional group is -OH, the hydroxyl
group, bonded to a tetrahedral carbon
• Nomenclature Rules
– Same as for Alkenes and Alkynes except you
only drop the -e, and add -ol!
OH
propane
propanol
Nomenclature of Alcohols
• 1) Select the longest chain that contains the
carbon bonded to the -OH group, and
number the chain to give the carbon bonded
to the -OH group the lowest number
• The -OH group takes precedence over
alkyl groups, double bonds, triple bonds,
and halogens!!!
Nomenclature of Alcohols
• 2) Change the suffix by dropping the -e, and
adding -ol. Use the number to show
location. In cycloalkanes, start numbering
from the carbon bonded to the -OH.
• 3) Name and number substituents and list
them in alphabetical order.
Naming Alcohols
1. The parent chain must contain the –OH group. Change
parent ending to “-ol”.
2. Give the –OH the lowest possible number.
7
2
6
4
3
5
OH
6,6-dimethyl-3-heptanol
1
Alcohol Nomenclature
CH3OH
CH3CH2OH
methanol
methyl alcohol
ethanol
ethyl alcohol
OH
CH3CHCH3 2º
2-propanol
isopropyl alcohol
1º
OH
CH3CCH3
3º
CH3
2-methyl-2-propanol
tert-butyl alcohol
OH > C=C > R, X
OH
CH3
CH3CHCH2CHCH3
Cl
4-methyl-2-pentanol
OH
CH3CHCH2CCH3
4-chloro-2-methyl-2-pentanol
CH3
Cl
OH
Cl
CH3CHCH2CCH2CHCH2CH3
CH3
2,6-dichloro-4-methyl-4-octanol
OH > C=C > R, X
OH
CH3CHCH2CH CH2
OH
4-penten-2-ol
Cl
CH3CHCH CHCHCH3
5-chloro-3-hexen-2-ol
Cl
CH3C CCH2OH
CH2CH3
3-chloro-2-ethyl-2-buten-1-ol
OH
What is the systematic name for this alcohol?
A) 2,3-diethyl-5,5-dimethyl-2-hexanol
B) 4,5-diethyl-2,2-dimethyl-5-hexanol
C) 4-ethyl-3,6,6-trimethyl-3-heptanol
D) 4-ethyl-2,2,5-trimethyl-5-heptanol
E) 1,2-diethyl-1,4,4,-trimethyl-1-pentanol
Naming Alcohols
3. When the –OH group is attached to a ring, it is assumed
to be at carbon #1.
OH
1
2
CH3
2-methylcyclopentanol
(NOT 2-methyl-1-cyclopentanol)
CH3
CH3
OH
CH2CH3
What is the systematic name for this alcohol?
A) 7-ethyl-3,3-dimethylcycloheptanol
B) 2-ethyl-6,6-dimethyl-1-cycloheptanol
C) 4-ethyl-1,1-dimethylcycloheptanol
D) 2-ethyl-6,6-dimethylcycloheptanol
E) 7-ethyl-3-dimethylcycloheptanol
Classification
• We classify alcohols as 1o, 2o, and 3o, depending
on the classification of the carbon they are
bonded to.
OH
OH
OH
Multiple -OH’s present
• Molecules with 2 -OH’s are named as diols
• Molecules with 3 -OH’s are named as triols
• (Note: you do not drop the -e when using
diol, triol, etc)
• Compounds with 2 -OH’s are refered to as
glycols
OH
HO
OH
HO
OH
Physical Properties of Alcohols
• The most important physical property is their
polarity
• Both the C-O bond and the O-H bond are polar
covalent bonds
• Thus alcohols are polar molecules
• They also have the ability to hydrogen bond.
• These factors lead to higher B.P’s, M.P’s. etc
Physical Properties of Alcohols
• Because of increase London forces (van der
Waals forces) between larger molecules, the B.P.
of all types of compounds, including alcohols,
increase as molecular weight increases
• Alcohols are much more soluble in H2O due to
their H-bonding capacity.
• As MW increases, the water solubility of alcohols
decreases
• This is because the hydrocarbon portion of the
molecule dominates.
Reactions of Alcohols
A) Acidity of Alcohols
-Alcohols are considerably weaker acids
than carboxylic acids, but can lose their
hydrogen in an acid-base reaction.
OH
+ Base
O
+ Base-H
Methanol
• Methanol was once prepared by the destructive
distillation of wood.
• Wood alcohol.
• Toxic, causes blindness in low doses (15 mL).
• Routinely used as a solvent and starting material.
• Methanol used by the chemical industry is
prepared by the catalytic reduction of carbon
monoxide.
CO + 2 H2
Cu/ZnO/Al2O3
250°C
CH3OH
Ethanol
• Prepared by the fermentation of grains and sugars.
• Grain alcohol.
• Used in alcoholic beverages.
• The largest single use of ethanol is as a motor fuel
and fuel additive (replaces MTBE).
• 5 billion gallons are prepared (primarily from corn)
annually in the U.S. for fuel uses.
• Ethanol used by the chemical industry is prepared
by the acid-catalyzed hydration of ethylene.
H2C=CH2 + H2O
H3PO4
250°C
CH3CH2OH
The Polar -OH Group
The physical properties of the alcohols are strongly
influenced by the polar -OH group.
Electrostatic
Potential Map
Neutral
methyl
group
Methanol
Negatively
polarized
oxygen
Positively
polarized
hydrogen
Boiling Points
The polar -OH group allows hydrogen bonding to
take place in alcohols. These strong intermolecular
forces result in higher than expected boiling points.
R
O
+
H
H +
O
H
+
R
O
+
H O
R
H
+
R
O
R
Compound
MW (g/mol)
BP (°C)
CH3CH2CH2CH3
58
-0.5
CH3CH2Cl
65
12.5
CH3CH2CH2OH
60
97
Ethers
• Structure- functional group is a Oxygen
bonded to 2 carbons
• Simplest ether is dimethyl ether
H3 C
O
CH3
Nomenclature of Ethers
• The common naming system is used for
simple ethers:
– List the alkyl groups bonded to the oxygen in
alphabetical order, followed by the work
“ether”.
H 3C
O
O
CH3
O
O
O
Ether Nomenclature
CH3CH2OCH2CH3
diethyl ether
CH3OCH2CH3
ethyl methyl ether
OCH3
cyclohexyl methyl ether
OCH2CH3
cyclooctyl ethyl ether
Crown Ethers
• Large rings consisting repeating (-OCH2CH2-) or similar
units
• Named as x-crown-y
– x is the total number of atoms in the ring
– y is the number of oxygen atoms
– 18-crown-6 ether: 18-membered ring containing 6
oxygens atoms
• Central cavity is electronegative and attracts cations
18-Crown-6
Uses of Crown Ethers
• Complexes between crown ethers and ionic salts are soluble in
nonpolar organic solvents
• Creates reagents that are free of water that have useful
properties
• Inorganic salts dissolve in organic solvents leaving the anion
unassociated, enhancing reactivity
Physical Properties of Ethers
• Ethers are polar compounds
• The oxygen has a partial minus charge, the
carbons bonded to the oxygen have a partial
positive charge
• Ether have very weak intermolecular forces
which results in low boiling points
The Ethers
Ethers lack the polar -OH group and therefore do
not have hydrogen bonding.
Electrostatic
Potential Map
Negatively
polarized
oxygen
Neutral
ethyl
group
Neutral
ethyl
group
Diethyl ether
Reactions of Ethers
• Like alkanes, they are resistant to most
chemical reactions
• Therefore, they are ideal to use as solvents
Diethyl Ether
• Was once widely used as an anesthetic.
• Highly flammable.
• Presently used as a solvent.
• Prepared
by
the
dehydration of ethanol.
2 CH3CH2OH
H2SO4
sulfuric
acid-catalyzed
CH3CH2OCH2CH3 + H2O
Boiling Points
Ethers have weak intermolecular forces, which
results in low boiling points. Low molecular weight
ethers are highly volatile.
Compound
MW (g/mol)
BP (°C)
CH3CH2OH
46
78.5
CH3OCH3
46
-25
CH3CH2CH2CH2OH
74
117.2
CH3CH2OCH2CH3
74
34.5
Alcohols & Ethers
Alcohols and ethers have very different chemical and
physical properties. This is due to the polar -OH
group that’s present in alcohols but absent in ethers.
Compound Polarity
ROH
ROR’
polar
nonpolar
HydrogenBonding?
BP
Reactive?
yes
high
yes
no
low
no
Uses
starting
materials
solvents
Oxidation and Reduction
O
Carboxylic Acid
RCOH
O
O
Aldehyde / Ketone RCH
RCR'
OH
OH
Alcohol
RCH2 RCR'
H
Alkane
RCH3 RCH2R'
O
X
I
D
A
T
I
O
N
Oxidation: Increase C-O bonds
Reduction: Increase C-H bonds
R
E
D
U
C
T
I
O
N
Common Reducing Agents
Sodium borohydride (NaBH4)
is a mild reducing agent.
O
RCH
OH
NaBH4
RCH2
aldehyde
1º alcohol
O
OH
RCR'
NaBH4
RCR'
H
ketone
2º alcohol
Common Reducing Agents
Lithium aluminum hydride (LiAlH4)
is a strong reducing agent.
O
RCOH
carboxylic
acid
OH
LiAlH4
RCH2
1º alcohol
Predict the Products
O
CH3CH2CH2CH
O
CH3CCH3
OH
NaBH4
NaBH4
CH3CH2CH2CH2
OH
CH3CCH3
H
O
CH3CH CHCOH
OH
LiAlH4
O
C OH
LiAlH4
CH3CH CHCH2
OH
CH2
Common Oxidizing Agents
Pyridinium chlorochromate (PCC)
(C5H6NCrO3Cl) is a mild oxidizing agent.
OH
RCH2
O
PCC
aldehyde
1º alcohol
OH
RCR'
RCH
O
PCC
RCR'
H
2º alcohol
ketone
Common Oxidizing Agents
Chromium trioxide (CrO3) and sodium dichromate
(Na2Cr2O7) are strong oxidizing agents.
OH
RCH2
1º alcohol
OH
RCR'
H
2º alcohol
CrO3
or
Na2Cr2O7
+
H3O
O
RCOH
carboxylic
acid
CrO3
or
Na2Cr2O7
+
O
RCR'
H3O
ketone
Predict the Products
O
CH3CH2CH2CH2CH2OH
PCC
CH3CH2CH2CH2CH
O
CH3CH2CH2CH2CH2OH
CrO3
CH3CH2CH2CH2COH
H 3O
O
OH
CH3CH2CH2CHCH3
Na2Cr2O7
CH3CH2CH2CCH3
H3O
OH
Na2Cr2O7
H 3O
O
The Williamson Ether Synthesis
2 ROH
alcohol
ROalkoxide
+
2M

2 ROM
M = Na, K
+ R’X
alkyl
halide

SN2
ROR’ + Xether
R can be 1º, 2º, 3º, or cycloalkyl.
R’ should be methyl or 1º.
+
H2
Synthesis of Diethyl Ether via the
Williamson Synthesis
Diethyl ether is a
symmetrical ether.
2 CH3CH2OH + 2 Na  2 CH3CH2ONa + H2
ethanol
CH3CH2
O-
ethoxide
ion
sodium ethoxide
+ CH3CH2I  CH3CH2OCH2CH3 + ISN2
ethyl
iodide
diethyl
ether
Synthesis of tert-Butyl Methyl
Ether via the Williamson Synthesis
tert-Butyl methyl ether is
an asymmetrical ether.
CH3
CH3
C O
CH3
nucleophile
SN2
CH3 I
This is the
better route
CH3
CH3
C O CH3
O
base
H CH2
C
I
CH3
I
CH3
tert-butyl methyl ether
CH3
CH3
+
E2
CH3
H 2C C
+ CH3OH + I
CH3
2-methylpropene