Chapters 5 & 6

Alcohols, Ethers, Thiols and Chirality

Chemistry 20

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 number of each substituent(alphabetical order) as a prefix to the name of the

main 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

OH │

CH3─CH─CH2─CH3 2-butanol

CH3

│

CH3─CH─CH ─CH2─OH 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

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

Chemical Properties of Alcohols

1. Acidity of Alcohols:

2. Acid-Catalyzed Dehydration:

CH3CH2OH CH2 = CH2 + H2OH2SO4

180°C

3. Oxidation of Alcohols:

C = C + H20Dehydration

Hydration- C – C -

H OH

OH NaOHH2O O-Na+ H2O+

Phenol Sodium phenoxide(a water-soluble salt)

+

Acid-Catalyzed Dehydration

CH3CH2OH CH2 = CH2 + H2OH2SO4

180°C

CH3CHCH3 CH2 = CH - CH2 + H2OH2SO4

140°C

CH3 C CH3 CH3 C = CH2 + H2OH2SO4

50°C

OH

OH

CH3 CH3

1°

2°

3°

High T

Moderate T

Low T

Ease of dehydration of alcohols

1° 2° 3°

Alkene having the greater number of alkyl groups on the double bond

generally predominates.

Acid-Catalyzed Dehydration

CH3CH2CHCH3

OH H3PO4 CH3CH=CHCH3 CH3CH2CH=CH21-Butene (20%)

2-Butene (80%)

2-Butanol

+-H2O

CH3CHCHCH3OH

CH3 H2SO4CH3C=CHCH3

CH3

CH3CHCH=CH2

CH3

3-Methyl-1-butene2-Methyl-2-butene (major product)

3-Methyl-2-butanol

+-H2O

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

Cyclic Ethers

Ethylene oxide Tetrahydrofuran (THF)

OO

One of the atoms in a ring is oxygen.

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

12345

123

CH3-CH-CH2-CH-CH-CH3 5-Chloro-3-methyl-2-hexanethiol

1234

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

2HOCH3CH2SH + 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.