Chapter 13 Alcohols and Phenols -...
Transcript of Chapter 13 Alcohols and Phenols -...
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