chapter 14 & 15 alcohols, ethers, thiols and chirality chemistry b11
TRANSCRIPT
Chapter 14 & 15
Alcohols, Ethers, Thiols and Chirality
Chemistry B11
Alcohols
Alcohols Contain a hydroxyl group (-OH).
Phenols Contain a benzene ring with a hydroxyl
group (-OH).
OH NaOHH2O O-Na+ H2O+
Phenol Sodium phenoxide(a water-soluble salt)
+OH
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)
Naming Alcohols
Step 1Select the longest carbon chain
that contains the -OH group.
Step 2Number from the end nearest -OH group.
Step 3Change the ending of parent alkane from -e to -ol.
Use the number to show the location of -OH.
Step 4Give the location and name of each substituent
(alphabetical order) as a prefix to the name of themain chain.
CH3─CH2─CH2─OH 1-Propanol
OH │CH3─CH─CH3 2-Propanol
CH3 OH │ │CH3─CH─CH2─CH2─CH─CH3 5-Methyl-2-hexanol
Naming Alcohols
123
123
123456
CH3─CH─CH2─CH─CH3 4-Nitro-2-pentanol
CH3─CH─CH ─CH─OH 1-Bromo-3-chloro-2-methyl-1-butanol
CH3
CH3─C─CH2─OH 2,2-dimethyl-1-propanol
Naming Alcohols
CH3
1234
123
1 2 3 4
Cl
5
NO2
BrCH3
OH
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 OHOH
1,2-Ethanediol
(Ethylene glycol)
1,2-Propanediol
(Propylene glycol)
1,2,3-Propanetriol
(Glycerol, Glycerin)
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
Different types of Alcohols
• Phenol is the IUPAC name for benzene with a hydroxyl group.
• Many are used as antiseptics and
disinfectants.
• Is a weak acid.
Phenol
Phenol
OH NaOHH2O O-Na+ H2O+
Phenol Sodium phenoxide(a water-soluble salt)
+
CH2CH3 CH3 CH=CH2
TolueneEthylbenzene Styrene
OH
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 ↓).
6. They are weak acids (weaker than Phenol).
OHpolar
nonpolar
C-O: (3.5 – 2.5 = 1.0) O-H : (3.5 – 2.1 = 1.4)
Chemical Properties of Alcohols
1. Acidity of Alcohols:
3. Oxidation of Alcohols:
2. Acid-Catalyzed Dehydration:
CH3CH2OH CH2 = CH2 + H2OH2SO4
180°C
C = C + H20Dehydration
Hydration- C – C -
H OH
OH NaOHH2O O-Na+ H2O+
Phenol Sodium phenoxide(a water-soluble salt)
+
In the oxidation [O] of a primary alcohol 1, one H isremoved from the –OH group and another H from the Cbonded to the –OH.
primary alcohol aldehyde
OH O │ ║ CH3─C─H CH3─C─H + H2O │ H
ethanol ethanal (ethyl alcohol) (acetaldehyde)
Oxidation of 1° Alcohols
K2Cr2O7
H2SO4
[O]
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
Oxidation of 2° Alcohols
[O]
K2Cr2O7
H2SO4
Tertiary 3 alcohols cannot be oxidized.
Tertiary alcohol no reaction
OH │
CH3─C─CH3 no product │
CH3 no H on the C-OH to oxidize
2-methyl-2-propanol
Oxidation of 3° Alcohols
K2Cr2O7
H2SO4
[O]
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
Oxidation of Alcohols in our body
[O] [O] [O]
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
Ethers
Physical Properties of Ethers
1. They are polar compounds (because of C-O).
2. Weak dipole-dipole interactions.
3. Low boiling points: hydrocarbons < ethers < alcohols.
4. More soluble in water than other hydrocarbons of similar molecular weight (H-bond with water).
δ-
δ+δ+
δ+(3.5 – 2.5 = 1)C-O
HO
Hδ+
δ-
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 CH3─CH2─S─H
Methanethiol Ethanethiol
Naming Thiols
Step 1Select the longest carbon chain
that contains the -SH group.
Step 2Number from the end nearest -SH group.
Step 3Add –thiol to the name of the parent alkane.Use the number to show the location of -SH.
Step 4Give the location and name of each substituent
(alphabetical order) as a prefix to the name of themain chain.
CH3
CH3CHCH2CH2CH2SH 4-Methyl-1-pentanethiol
CH3
CH3CHCH2SH 2-Methyl-1-propanethiol
CH3-CH-CH2-CH-CH-CH3 5-Chloro-3-methyl-2-hexanethiol
1234
12345
123
CH3Cl
56
SH
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 CH3CH2S-Na+ + H2OH2O
2. Oxidation to disulfides: -S-S- disulfide
2OHCH3CH2SH + O2 HOCH2CH2S-SCH2CH2OHOxidation
Reduction
Sodium ethanethiolate
Chirality
sameconnectivity
Stereoisomers
Chiral
Enantiomers Diastereomers
Constitutional Isomers
Cis-Trans Isomers
withstereocenters
without stereocenters
Achiral
differentconnectivity
Isomers
A
Original molecule Mirror image
OH
CH3C CH3
H
OH
CCH3
HH3C
OH
CH3C CH3
H
The mirror imagerotated by 120°
120° rotate by 120°about the
C-OH bond
This means that the original and its mirror image are the similar molecules.
Achiral
superposable mirror images
2-propanol
Enantiomers (chiral)
They have different chemical and physical properties.
Original molecule
OH
CH3C CH2CH3
H
OH
CCH3
HCH3CH2
OH
CH3C H
CH2CH3
Mirror image The mirror imagerotated by 180°
180° rotate by 180°about the
C-OH bond
nonsuperposable mirror images
2-butanol
A carbon with four different groups bonded to it.
stereocenterstereocenter
It usually creates enantiomers.