Alcohols, Ethers, Thiols and Chirality

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Chemistry B11
Chapter 14 15 Alcohols, Ethers, Thiols and
Chirality
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Alcohols
Alcohols Contain a hydroxyl group
(-OH). Phenols Contain a benzene ring with a
hydroxyl group (-OH).
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Naming Alcohols

• IUPAC name We replace the -e in alkane name with
  -ol.
• Common name As simple alcohols using the name of
  the alkyl group followed by alcohol.
• CH4 methane
• CH3-OH methanol (methyl alcohol)
• CH3-CH3 ethane
• CH3-CH2-OH ethanol (ethyl alcohol)

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Naming Alcohols
Step 1 Select the longest carbon chain that
contains the -OH group.
Step 2 Number from the end nearest -OH group.
Step 3 Change the ending of parent alkane from -e
to -ol. Use the number to show the location of
-OH.
Step 4 Give the location and name of each
substituent (alphabetical order) as a prefix to
the name of the main chain.
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Naming Alcohols
CH3-CH2-CH2-OH 1-propanol OH
CH3-CH-CH3 2-propanol CH3
OH
CH3-CH-CH2-CH2-CH-CH3 5-methyl-2-hexanol
1
2
3
3
1
2
5
1
2
3
4
6
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Naming Alcohols
OH CH3-CH-CH2-CH3
2-butanol CH3
CH3-CH-CH -CH2-OH 3-chloro-2-m
ethyl-1-butanol CH3
CH3-C-CH2-OH 2,2-dimethyl-1-propano
l
1
2
3
4
Cl
1
2
3
4
CH3
1
2
3
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Diols Triols
Diol a compound containing two OH (Hydroxyl
groups). Triol a compound containing three OH
(Hydroxyl groups).
CH2 CH2
CH2 CH CH2
CH3 CH CH2
OH
OH
OH
OH
OH
OH
OH
1,2-Ethanediol (Ethylene glycol)
1,2-Propanediol (Propylene glycol)
1,2,3-Propanetriol (glycerol, glycerin)
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Different types of Alcohols
Primary (1º) Secondary (2º ) Tertiary
(3º) H CH3 CH3

CH3-C-OH CH3-C-OH CH3-C-OH

H
H
CH3 1 C 2 C 3 C
attached attached attached to
C-OH to C-OH to C-OH
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Phenol

• Phenol is the IUPAC name for benzene with a
  hydroxyl group.
• Many are used as antiseptics and disinfectants.
• Is a weak acid.

OH
Phenol
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Physical Properties of Alcohols

• Alcohols are polar molecules (because of O-H and
  C-O).
• Hydrogen bonding between alcohols molecules.
• Have higher boiling point than Alkanes, Alkenes
  Alkynes.
• Molecular weight ? London dispersion forces ?
  bp ?
• More soluble in water (Molecular weight ?
  solubility ?).
• They are weak acids (weaker than Phenol).

polar
nonpolar
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Chemical Properties of Alcohols
1. Acidity of Alcohols
2. Acid-Catalyzed Dehydration
H2SO4
CH3CH2OH
CH2 CH2 H2O
180C
Dehydration
C C H20
- C C -
Hydration
H
OH
3. Oxidation of Alcohols
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Oxidation of 1 Alcohols
In the oxidation O of a primary alcohol 1?, one
H is removed from the OH group and another H
from the C bonded to the OH.
primary alcohol aldehyde
OH O

CH3-C-H CH3-C-H H2O
H ethanol
ethanal (ethyl alcohol)
(acetaldehyde)
O
K2Cr2O7
H2SO4
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Oxidation of 2 Alcohols
The oxidation of 2? alcohols is similar to 1,
except that a ketone is formed.
secondary
alcohol ketone OH O
CH3-C-CH3
CH3-C-CH3 H2O
H 2-propanol
2-propanone
O
K2Cr2O7
H2SO4
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Oxidation of 3 Alcohols
Tertiary 3? alcohols do not oxidize.
Tertiary alcohol no reaction
OH
CH3-C-CH3 no product

CH3 no H on the C-OH to
oxidize 2-methyl-2-propanol
O
K2Cr2O7
H2SO4
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Oxidation of Alcohols in our body

• In the body
• Enzymes in the liver oxidize ethanol.
• Blood alcohol over 0.4 can be fatal.
• O O
• CH3CH2OH CH3CH CH3COH
  2CO2 H2O Energy
• ethanol ethanal
  acetic acid

O
O
O
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Ethers
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Ethers

• An ether
• Contains an -O- between two carbon atoms.
• Is named from alkyl names of the attached groups
• (in alphabetical order) followed by ether.
• CH3-O-CH3 CH3-CH2-O-CH3
• dimethyl ether ethyl methyl ether

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Physical Properties of Ethers

• They are polar compounds (because of C-O).
• Weak dipole-dipole interaction.
• Low boiling point alkanes lt ethers lt alcohols.
• More soluble in water than other hydrocarbons
• of similar molecular weight (H-bond with water).

(3.5 2.5 1)
C-O
H
O
d
H
d-
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Chemical Properties of Ethers
Ethers are resistance to chemical reactions
(inert).
Oxidation
Reduction
Good solvent for organic reactions.
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Thiols
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Thiols

• An Thiol
• Contains an SH (sulfhydryl) group.
• Is named by selecting the longest carbon chain
  that contain the -SH. We add -thiol to the name
  of the parent alkane.
• Parent chain is numbered from the end nearest to
• the -SH group.
• CH3-S-H CH3-CH2-S-H
• Methanethiol Ethanethiol

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CH3
CH3CHCH2CH2CH2SH
4-Methyl-1-pentanethiol
5
2
3
4
1
CH3
CH3CHCH2SH
2-Methyl-1-propanethiol
2
1
3
CH3
Cl
CH3-CH-CH2-CH2-CH-CH2-SH
5-Chloro-2-methyl-1-hexanethiol
1
2
3
4
5
6
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Physical Properties of Thiols

• They have unpleasant odors.
• They are nonpolar compounds.
• S-H (2.5 2.1 0.4) nonpolar covalent.
• 3. Low boiling point (London dispersion forces).
• 4. Almost insoluble in water.

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Chemical Properties of Thiols
1. Thiols are weak acids (react with strong
bases).
H2O
CH3CH2SH NaOH CH3CH2S-Na H2O
Sodium ethanethiolate
2. Oxidation to disulfides -S-S- disulfide
Oxidation
2CH3CH2SH O2 HOCH2CH2S-SCH2CH2OH
Reduction
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Chirality
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A
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Achiral
superposable mirror images
2-propanol
This means that the original and its mirror image
are the similar molecule.
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Enantiomers (chiral)
nonsuperposable mirror images
2-butanol
They have different chemical and physical
properties.
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stereocenter
A carbon with four different groups bonded to it.
It usually creates enantiomers.