Transcript Ch. 14 Alcohols, Ethers, & Thiols

Ch. 14 Alcohols, Ethers, &
Thiols
Note: We are skipping Ch 13
HW-14.10, 14.11, 14.13, 14.14,
14.22, 14.33, 14.35,14.37, 14.43,
14.45, 14.54, 14.71
Alcohols, Ethers, & Thiols
• Alcohols and Ethers are two classes of
oxygen containing organic compounds
• Thiols are a class of Sulfur containing
organic compounds
• Thiols are like alcohols, only they have a
-SH functional group instead of an -OH
Examples
• Alcohol- Ethanol- gas additive,
alcohol consumed by
OH
humans
important solvent
• Ether- Diethyl ether- 1st anesthetic
important solvent
O
• Thiol- Ethanethiol- additive to natural gas
SH
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.
Examples
OH
OH
OH
OH
Br
OH
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 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
Reactions of Alcohols
B) Acid catalyzed dehydration
-Converts alcohols to alkenes by
eliminating a molecule of water from
adjacent carbons
When the equivalent of a molecule of water is
removed from a compound, it is called a
Dehydration Reaction
Dehydration of Alcohols
• 1o alcohols are more difficult to dehydrate.
They require high temperatures in
concentrate H2SO4
• 2o alcohols require lower temperatures
• 3o alcohols are the easiest to dehydrate and
undergo dehydration only slightly above
room temperature
Examples
H2SO4
OH
OH
180oC
CH2
+ H 2O
H2SO4
140oC
H2SO4
OH
H2C
180oC
50oC
+ H 2O
+ H 2O
Prediction of Product
• When the dehydration of an alcohol can
yield more than one different double bond,
the most substituted double bond will form.
H2SO4
+
heat
OH
80%
20%
Recap
• Earlier, we learned the acid catalyzed
hydration of alkenes
OH
H2C
CH2
+ H2O
acid
H2C
H
CH2
• Now we are saying alcohols can be
dehydrated with acid
OH
H2C
H
CH2
acid
heat
H2C
CH2
+ H2O
Equilibrium Reactions
• The fact is that these reactions are reversible
• Alkene hydration and alcohol dehydration
are competing reactions and the following
equilibrium exist:
hydration
H2C
CH2 + H2O
dehydration
OH
H2C
H
CH2
Controlling Equilibriums
• Equilibriums are governed by Le
Chatelier’s Principle
• Le Chatelier’s Principle- when external
stress is applied to a system at equilibrium,
the system will react to relieve the stress
Controlling Equilibriums
• We can control the hydration/dehydration
equilibrium by:
– Using large amounts of water (favors alcohol
formation)
– Using concentrated acids (favors alkene
formation
– Removal of water as it forms (favors alkene
formation)
Reactions of Alcohols
C) Oxidation of 1o and 2o alcohols
-Remember, oxidation in organic chemistry is
defined as the increase in C-O bonds and/or
the decrease in C-H bonds
O
O
[O]
[O]
OH
H
OH
Oxidation of Alcohols
• The reagent used for the oxidation of
alcohols is potassium dichromate, K2Cr2O7,
dissolved in H2SO4
O
O
K2Cr2 O7
K2Cr2 O7
OH
H2SO4
H
H2SO4
• The reaction proceeds to form the
carboxylic acid unless the aldehyde is
removed
OH
Oxidation of Alcohols
• The oxidation of 2o alcohols results in a
ketone
OH
K2Cr2 O7
O
H2SO4
• 3o alcohols can not be oxidized because the
carbon bonded to the -OH is bonded to 3
other carbons.
Ethers
• Structure- functional group is a Oxygen
bonded to 2 carbons
• Simplest ether is dimethyl ether
H3C
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
Physical Properties
• 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
Reactions of Ethers
• Like alkanes, they are resistant to most
chemical reactions
• Therefore, they are ideal to use as solvents
Thiols
• The most outstanding property of low
molecular weight thiols is their stench!!
• They are responsible for the wonderful
odors from skunks, rotten eggs, sewage, and
paper mills
• Structure- functional group is -SH, the
sulfhydryl group, bonded to a tetrahedral
carbon
Naming Thiols
• Name just like alcohols, except add -thiol
instead of -ol and don’t drop the -e.
• Find longest chain containing -SH, number
to give -SH lowest number.
SH
SH
SH
Physical Properties
• Very little difference in electronegativity
between Sulfur and Carbon, so the bond is
actually nonpolar
• They DO NOT hydrogen bond
• They have low boiling points and very little
water solubility
Reactions of Thiols
• Thiols are weak acids and react with bases
to lose a proton.
SH
+ NaOH
S
Na
+ H2O