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Chemistry 20
Chapters 5 & 6
Alcohols, Ethers, Thiols and Chirality
Alcohols
Alcohols
Contain a hydroxyl group (-OH).
Phenols
Contain a benzene ring with a hydroxyl
group (-OH).
OH
OH + NaOH
Phenol
H2 O
O- Na +
+
S od ium phenoxide
(a w ater-soluble salt)
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
CH3─CH3
ethane
CH3─CH2─OH
ethanol
(methyl alcohol)
(ethyl alcohol)
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 number of each substituent
(alphabetical order) as a prefix to the name of the
main chain.
Naming Alcohols
3
1
2
CH3─CH2─CH2─OH
1-propanol
OH
│
CH3─CH─CH3
2-propanol
3
2
1
CH3
OH
│
│
CH3─CH─CH2─CH2─CH─CH3
6
5
4
3
2
1
5-methyl-2-hexanol
Naming Alcohols
OH
│
CH3─CH─CH2─CH3
1
2
3
2-butanol
4
CH3
│
CH3─CH─CH ─CH2─OH
Cl
4
3
2
3-chloro-2-methyl-1-butanol
1
CH3
CH3─C─CH2─OH
CH3
3
2
1
2,2-dimethyl-1-propanol
Diols & Triols
Diol: a compound containing two –OH (Hydroxyl groups).
Triol: a compound containing three –OH (Hydroxyl groups).
CH2 – CH2
OH
OH
CH3 – CH – CH2
OH
OH
CH2 – CH – CH2
OH
OH
OH
1,2-Ethanediol
1,2-Propanediol
1,2,3-Propanetriol
(Ethylene glycol)
(Propylene glycol)
(glycerol, glycerin)
Different types of Alcohols
Primary (1º)
Secondary (2º )
H
│
CH3─C─OH
│
H
CH3
│
CH3─C─OH
│
H
1C
2C
attached
to C-OH
attached
to C-OH
Tertiary (3º)
CH3
│
CH3─C─OH
│
CH3
3C
attached
to C-OH
Phenol
• Phenol is the IUPAC name for
benzene with a hydroxyl group.
OH
CH2 CH3
• Many are used as antiseptics and
Eth
ylb enzene
Phenol
disinfectants.
• Is a weak acid.
OH + NaOH
Phenol
H2 O
O- Na+ + H2 O
S od ium phenoxide
(a w ater-soluble salt)
Physical Properties of Alcohols
1. Alcohols are polar molecules (because of O-H and C-O).
2. Hydrogen bonding between alcohols molecules.
3. Have higher boiling points than Alkanes, Alkenes, and Alkynes.
4. Molecular weight ↑ : London dispersion forces ↑ : bp ↑
5. More soluble in water (Molecular weight ↑ : solubility ↓).
nonpolar
6. They are weak acids (weaker than Phenol).
polar
OH
Chemical Properties of Alcohols
1. Acidity of Alcohols:
H2 O
OH + NaOH
Phenol
O- Na+ + H2 O
S od ium phenoxide
(a w ater-soluble salt)
2. Acid-Catalyzed Dehydration:
CH3CH2OH
-C–CH OH
H2SO4
180°C
CH2 = CH2 + H2O
Dehydration
Hydration
C = C + H20
3. Oxidation of Alcohols:
Acid-Catalyzed Dehydration
1°
CH3CH2OH
H2SO4
180°C
CH2 = CH2 + H2O
High T
CH2 = CH - CH2 +
H 2O
Moderate T
CH3 C = CH2 + H2O
Low T
OH
2°
CH3CHCH3
H2SO4
140°C
OH
3°
CH3 C CH3
CH
H2SO4
50°C
CH
3
3
1°
2°
3°
Ease of dehydration of alcohols
Acid-Catalyzed Dehydration
Alkene having the greater number of alkyl groups on the double bond
generally predominates.
OH
CH3 CH2 CHCH3
2-Butanol
H3 PO4
-H2 O
CH3 CH=CHCH3 + CH3 CH2 CH=CH2
2-Bu tene
1-Butene
(80%)
(20%)
CH3
CH3
CH3
H2 SO4
CH3 CHCHCH3
CH3 C=CHCH3 + CH3 CHCH=CH2
-H2 O
OH
3-Meth yl-2-b utanol
2-Methyl-2-b utene 3-Methyl-1-bu tene
(major prod uct)
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
OH
│
CH3─C─H
│
H
ethanol
(ethyl alcohol)
[O]
K2Cr2O7
H2SO4
aldehyde
O
║
CH3─C─H + H2O
ethanal
(acetaldehyde)
Oxidation of 2° Alcohols
The oxidation of 2 alcohols is similar to 1°, except that a
ketone is formed.
[O]
secondary alcohol
OH
│
CH3─C─CH3
│
H
2-propanol
K2Cr2O7
H2SO4
ketone
O
║
CH3─C─CH3 + H2O
2-propanone
Oxidation of 3° Alcohols
Tertiary 3 alcohols cannot be oxidized.
Tertiary alcohol
OH
│
CH3─C─CH3
[O]
no reaction
K2Cr2O7
H2SO4
no product
│
CH3
no H on the C-OH to oxidize
2-methyl-2-propanol
Oxidation of Alcohols in our body
In the body:
• Enzymes in the liver oxidize ethanol.
• Blood alcohol over 0.4% can be fatal.
CH3CH2OH
ethanol
[O]
O
║
CH3CH
ethanal
[O]
O
║
CH3COH
acetic acid
[O]
2CO2 + H2O + Energy
Ethers
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
Cyclic Ethers
One of the atoms in a ring is oxygen.
O
Eth ylene oxide
O
Tetrahydrofu ran
(THF)
Physical Properties of Ethers
1. They are polar compounds (because of C-O).
C-O
(3.5 – 2.5 = 1)
δ+
2. Weak dipole-dipole interactions.
δ+
δ+
δ-
3. Low boiling points: Hydrocarbons < ethers < alcohols.
4. More soluble in water than other hydrocarbons
of similar molecular weight (H-bond with water).
H
δ+
H
δ-
O
Chemical Properties of Ethers
Ethers are resistant to chemical reactions (inert).
Oxidation
Reduction
Good solvent for organic reactions.
Thiols
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
Methanethiol
CH3─CH2─S─H
Ethanethiol
Naming Thiols
Step 1
Select the longest carbon chain
that contains the -SH group.
Step 2
Number from the end nearest -SH group.
Step 3
Add –thiol to the name of the parent alkane.
Use the number to show the location of -SH.
Step 4
Give the location and name of each substituent
(alphabetical order) as a prefix to the name of the
main chain.
CH3
CH3CHCH2CH2CH2SH
5
4
3
2
4-Methyl-1-pentanethiol
1
CH3
CH3CHCH2SH
2
3
2-Methyl-1-propanethiol
1
CH3 SH
Cl
CH3-CH-CH2-CH-CH-CH3
6
5
4
3
2
1
5-Chloro-3-methyl-2-hexanethiol
Physical Properties of Thiols
1. They have unpleasant odors.
2. They are nonpolar compounds.
S-H
(2.5 – 2.1 = 0.4)
nonpolar covalent.
3. Low boiling points (London dispersion forces).
4. Almost insoluble in water.
Chemical Properties of Thiols
1. Thiols are weak acids (react with strong bases).
CH3CH2SH + NaOH
H2O
CH3CH2S-Na+ + H2O
Sodium ethanethiolate
2. Oxidation to disulfides:
-S-S- disulfide
Oxidation
2HOCH3CH2SH + O2
Reduction
HOCH2CH2S-SCH2CH2OH
Chirality
Isomers
same different
connectivity connectivity
Stereoisomers
without
stereocenters
with
stereocenters
Chiral
Achiral
Cis-Trans Isomers
Constitutional Isomers
Enantiomers
Diastereomers
A
Achiral
superposable mirror images
OH
C H
H3 C
CH3
Origin al molecu le
2-propanol
120° OH
H C CH
3
H3 C
Mirror image
rotate by 120°
about th e
C-OH bond
OH
C H
H3 C
CH3
The mirror image
rotated b y 120°
This means that the original and its mirror image are the similar molecules.
Enantiomers (chiral)
nonsuperposable mirror images
OH
C H
H3 C
CH2 CH3
Original molecule
2-butanol
180°
OH
H C CH
3
CH3 CH2
Mirror image
rotate by 180°
about the
C-OH b on d
OH
C CH CH
2
3
H3 C
H
The mirror image
rotated b y 180°
They have different chemical and physical properties.
stereocenter
A carbon with four different groups bonded to it.
It usually creates enantiomers.