Chapter 13Alcohols and Phenols

Alcohols and PhenolsStructure and Physical Properties

Alcohols, Ethers, Phenols

Structure of Functional Groups

Structure of Functional Groups

Alcohols, Ethers, Phenols

Structure of Functional Groups

In water, the H-O-H bond angle is 104.5° due to repulsion of the bonding electron pairs by the larger non-bonding electron pairs.

In alcohols, phenols, and ethers the corresponding bond angles are closer to the expected tetrahedral 109.5° due to the replacement of one or both hydrogen atoms by larger carbon atoms.

Alcohols, Ethers, Phenols

Common Names of Alcohols

Isomerism in Alcohols

1-propanol 2-propanol

Subclassification of Alcohols

Subclassification of Alcohols

Subclassification of Alcohols

AlcoholsNomenclature

Nomenclature of Alcohols

closest to the

Nomenclature of Alcohols

OH

OHOH

OHOH

A

B C

DE

2-heptanol

2-ethyl-3-methyl-1-butanol

2-methyl-2-propanol 2,2-dimethyl-1-propanol

2-ethyl-5-methyl-cyclohexanol

Alcohols and PhenolsPhysical Properties

Physical Properties of AlcoholsBoiling points increase with molecular weight

and decrease with branching.

Boiling points are higher than alkanes of similar molecular weight.

H3CCH2

H2C

CH2H2C

CH2H2C

CH3

H3CCH2

H2C

CH2H2C

CH2H2C

CH3

H3CCH2

H2C

CH2H2C

CH2H2C

CH3

H3CCH2

H2C

CH2H2C

CH2H2C

CH3

H3CCH2

H2C

CH2H2C

CH2H2C

CH3

Octane, boiling point = 126 °C

Attractive forces between alkane molecules are limited to simple London forces.

H3CCH2

H2C

CH2H2C

CH2H2C

O

H3CCH2

H2C

CH2H2C

CH2H2C

O

H3CCH2

H2C

CH2H2C

CH2H2C

O

H3CCH2

H2C

CH2H2C

CH2H2C

O

H3CCH2

H2C

CH2H2C

CH2H2C

OH H H HH

Heptanol, boiling point = 176 °C

Attractive forces between alcohol molecules include both dispersion forces and relatively strong hydrogen bonding.

Physical Properties of Alcohols

Alcohols are more water soluble than alkanes, but their water solubility is limited by the size of the

nonpolar portion of the molecule.

CH3O

H

H3CCH2

CH2CH2

CH2CH2

CH2O

H

Nonpolar, or hydrophobic portions

of moleculesPolar, or hydrophilic portions of molecules

Physical Properties of Alcohols

Physical Properties of Alcohols-Solubility

Physical Properties of Alcohols-Solubility

CH3

OH

CH3

OH

HO

H

THE RELATIVELY SMALL ATTRACTION BETWEENMETHANOL MOLECULES MAKES IT EASY FORWATER TO SEPARATE INDIVIDUAL METHANOL

MOLECULES FROM EACH OTHER AND DISSOLVE THE ALCOHOL.

METHANOL IS VERY SOLUBLE IN WATER.

H3CCH2

CH2CH2

CH2

CH2CH2

OH

H3CCH2

CH2CH2

CH2

CH2CH2

OH

HO

H

THE RELATIVELY LARGE ATTRACTION BETWEEN

HEPTANOL MOLECULES MAKES IT DIFFICULT FOR

WATER TO SEPARATE INDIVIDUAL HEPTANOL

MOLECULES FROM EACH OTHER AND DISSOLVE THE ALCOHOL. HEPTANOL IS VERY SLIGHTLY

SOLUBLE IN WATER.

Alcohols and PhenolsAcidity

ClH Cl

H3CC

O

O

H H3CC

O

O

Ar OH

Ar O

Alkyl OH

Alkyl O

R C C H R C C

R N

H

H R N

H

R C

H

H

H

R C

H

H

Functional group Example pKa Acid Strength Conjugate base Base strength

Mineral Acid -8

Carboxylic Acid 5

Phenol 10

Alcohol 16

Alkyne 25

Amine ~35

Alkane ~50

Short pKa Table

Alcohols - Acidity

Alkoxide Salts Formed by an Oxidation-Reduction Reaction

H3C CH2O H

Na

H3C CH2O H

Na

H3C CH2O H

Na

H3C CH2O H

Na

H3C CH2O

Na+ H22

H3C CH2O H

Na

H3C CH2O H

Na

H3C CH2O H

Na

H3C CH2O H

Na

H3C CH2O

Na+ H22

H3C CH2O H

Na

H3C CH2O H

Na

H3C CH2O H

Na

H3C CH2O H

Na

H3C CH2O

Na+ H22

Phenols - Structure

General Structure - A “hydroxyl” (OH) group attached directly to an aromatic ring:

OH OH

Phenol β-Naphtholα-Naphthol

OH

CH2 OH

Note:is not a phenol.

OH

ClBr

OH

NO2

OH

Cl

OH

Br

Br

OH

CH32-nitrophenol

orortho-nitrophenol

3-chlorophenolor

meta-chlorophenol

4-methylphenolor

para-methylphenol

2,4-dibromophenol

4-bromo-2-chloro-5-isopropyl-phenol

Phenols are named as aromatic compounds, using the ortho-, meta-, and para- prefixes or appropriate numbering.

1 1

1

1

2

1

Phenols - Nomenclature

Phenols - Physical Properties

Low Melting SolidsSoluble in Nonpolar SolventsAlso, Quite soluble in Water

OH OH

OH

OH

OH

Name Phenol Catechol Resorcinol

M.P. 40.5 ºC 105 ºC 110 ºC

Solubility 8.3 g/100mL 43 g/100mL 110 g/100mL in water

Phenols - Acidity

In water, phenol dissociates slightly as a weak acid. (Another name for phenol itself is “carbolic acid”)

OH O

+ H2O + H3O +

_

Acid Base Base Acid

How acidic is Phenol?pKa = A general measure of acidity.

The lower the pKa, the stronger the acid.

! ! Compound pKa

Methanol 16 Water 15.7 Phenol 9.9 Acetic Acid 4.8

Phosphoric Acid -2.1 Hydrochloric Acid -7

nonacids

weak acids

strong acids

Phenols - Acidity

OH OH

OH

NH2

OH

ClOH

CH3

OH

NO O

OH

O

CH3

OH

NO O

N

O

O

OH OH

NO O

N

O

ON

O

O

pKa=18 pKa=10

pKa=10.5 pKa=9.2

pKa=10.3 pKa=7.2

pKa=10.2 pKa=4.1

pKa=10 pKa=0.3

Phenols - Chemical Properties

OH

OH

O

O

+ 2 H .

OXIDATION

REDUCTION

O-Na+OH

+ NaOH + HOH

Acid-BaseReactions

Phenol Sodium phenoxide

Hydroquinone Paraquinone

Oxidation-ReductionReactions

Phenols - Examples of Important Compounds

o-phenyl phenol n-hexylresorcinol

butylated hydroxy anisole(BHA)

butylated hydroxy toluene(BHT)

OH

OH

OCH3

OH

OH

CH2CH2CH2CH2CH2CH3

OH

CH3