Organic Chemistry II

CHEM 271

Chapter OneAlcohols, Diols and Thiols

Nomenclature of Alcohols

Functional Class Nomenclature of Alcohols( Common Names)

Name the alkyl group and add "alcohol" as aseparate word.

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CHCH33CHCH22OHOH

CHCH33CHCHCHCH22CHCH22CHCH22CHCH33

OHOH

CHCH33CCHCCH22CHCH22CHCH33

OHOH

CHCH33

Ethyl alcoholEthyl alcohol

1-Methylpentyl alcohol1-Methylpentyl alcohol

1,1-Dimethylbutyl1,1-Dimethylbutylalcoholalcohol

IUPAC Nomenclature of Alcohols•Name as "alkanols." Replace –e ending of alkanename by -ol.•Number chain in direction that gives lowest numberto the carbon that bears the —OH group.

CHCH33CHCH22OHOH

CHCH33CHCHCHCH22CHCH22CHCH22CHCH33

OHOH

CHCH33CCHCCH22CHCH22CHCH33

OHOH

CHCH33

EthanolEthanol

2-Hexanol2-Hexanol

2-Methyl-2-pentanol2-Methyl-2-pentanol

Name these:

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CH3 CH

CH3

CH2OH

CH3 C

CH3

CH3

OH

CH3 CH

OH

CH2CH32-methyl-1-propanol

2-methyl-2-propanol

2-butanol

OH

Br CH3

3-bromo-3-methylcyclohexanol =>

Unsaturated Alcohols

Number the chain in thedirection that gives the lowest number to the carbon that bears the OH group

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4-penten-2-ol (old)

pent-4-ene-2-ol =>

CH2 CHCH2CHCH3

OH

Naming Priority

• Acids• Esters• Aldehydes• Ketones• Alcohols• Amines

• Alkenes• Alkynes• Alkanes• Ethers• Halides

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Chapter 10 8

Hydroxy Substituent

• When -OH is part of a higher priority class of compound, it is named as hydroxy.

• Example:

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CH2CH2CH2COOH

OH

4-hydroxybutanoic acid =>

Classes of Alcohols

• Primary: carbon with –OH is bonded to one other carbon. -CH2OH

• Secondary: carbon with –OH is bonded to two other carbons. -CHOH

• Tertiary: carbon with –OH is bonded to three other carbons. -COH =>

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CH3 CH

CH3

CH2OH CH3 C

CH3

CH3

OH

CH3 CH

OH

CH2CH3 =>

Diols

• Two numbers are needed to locate the two -OH groups.

• Use -diol as suffix instead of -ol.

Chapter 10 13

HO OH

1,6-hexanediol

=>

Glycols

• 1, 2 diols (vicinal diols) are called glycols.• Common names for glycols use the name of the

alkene from which they were made.

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CH2CH2

OH OH

CH2CH2CH3

OH OH

1,2-ethanediol

ethylene glycol

1,2-propanediol

propylene glycol =>

Glycrol• 1, 2,3 Triols are called glycrol>

CH2CHCH2

OHOH OH

Thiols

• 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 tothe -SH group.

Methanethiol Ethanethiol

CH3─S─H CH3─CH2─S─H

Physical Properties of Alcohols

1. Alcohols are polar molecules (because of O-H and C-O).

2. Have higher boiling point than Alkanes, Alkenes & Alkynes due to Hydrogen bonding involves oxygen of one molecule and hydrogen of another in alcohol molecules.

3. As the molecular weight increase, boiling point decrease.

4. As the molecular weight increase, solubility in water decrease .

5. The solubility of alcohols in water is due to hydrogen bonding between alcohol and water molecules.

6. They are weak acids (weaker than Phenol).

PHYSICAL PROPERTIES OF ALCOHOLS, cont.• The –OH group can hydrogen bond between alcohol molecules

leading to relatively high boiling points.• Hydrogen bonding in pure ethanol:

PHYSICAL PROPERTIES OF ALCOHOLS• The –OH group is polar and capable of hydrogen bonding.• This makes low molecular weight alcohols highly soluble in

water.• Hydrogen bonding in a water-methanol solution:

Acidity of Alcohols

pKa range: 15.5-18.0 (water: 15.7)Acidity decreases as alkyl group

increases.Halogens increase the acidity.Phenol is 100 million times more acidic

than cyclohexanol!

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Chapter 10 21

Preparation of Alcohols by Hydration of Alkenes

Water molecule add to double bond in accordance with Markovnikov’s rule

Preparation of Alcohols by Grignard ReagentsBy reaction of grignard reagents with aldehydes and

ketones to form Primary, Secondary and Tertialy Alcohols.

CH3CH2MgBr + C

H

H

O CH3CH2CH2OH

primary alcohol

CH3CH2MgBr + C

H

H3C

O CH3CH2CHOH

Secondry alcohol

CH3

CH3CH2MgBr + C

H3C

H3C

O CH3CH2COH

Tertiary alcohol

Ether

H3O+

Ether

H3O+

Ether

H3O+

CH3

CH3

Preparation of Alcohols by Reduction of Aldehydes and Ketone

Preparation of Alcohols by reduction of Carboxylic acids and Esters

Preparation of Alcohols from Epoxides

Preparation of Diols

Diols formed by reduction of dialdehyde by catalytic hydrogenation as the following reaction.

Mechanism of Reaction

By the reaction of alkyl halide with thiourea to give thiol compound

Preparation of Thiols

1- Reaction with Hydrogen Halide

Reactions of Alcohols

2- Reaction with Thionyl Chloride

3- Acid Catalyzed Dehydration

4- Conversion of Alcohols to Ethers

By Heating primary alcohols in the presence of Sulfuric acid (Condensation reaction)

5- Esterification

6- Oxidation of Alcohols

PCC : Pyridinium Chlorochromate

Primary alcohol is oxidized under strong or mild oxidizing agents to give acid or aldehyde

Oxidative Cleavage of Vicinal Diols

Reaction of Diols

Reactions of Thiols

Thiols are weak acids but more acidic than alcohols.

2- Oxidation of Thiols