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

  • Chapter 13 Alcohols and Phenols

  • Alcohols and Phenols Structure 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

  • Alcohols Nomenclature

  • Nomenclature of Alcohols

    closest to the

  • Nomenclature of Alcohols

  • OH

    OH OH

    OH OH

    A

    B C

    D E

    2-heptanol

    2-ethyl-3-methyl-1-butanol

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

    2-ethyl-5-methyl-cyclohexanol

  • Alcohols and Phenols Physical Properties

  • Physical Properties of Alcohols Boiling points increase with molecular weight

    and decrease with branching.

    Boiling points are higher than alkanes of similar molecular weight.

    H3C CH2

    H2C

    CH2 H2C

    CH2 H2C

    CH3

    H3C CH2

    H2C

    CH2 H2C

    CH2 H2C

    CH3

    H3C CH2

    H2C

    CH2 H2C

    CH2 H2C

    CH3

    H3C CH2

    H2C

    CH2 H2C

    CH2 H2C

    CH3

    H3C CH2

    H2C

    CH2 H2C

    CH2 H2C

    CH3

    Octane, boiling point = 126 °C

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

    H3C CH2

    H2C

    CH2 H2C

    CH2 H2C

    O

    H3C CH2

    H2C

    CH2 H2C

    CH2 H2C

    O

    H3C CH2

    H2C

    CH2 H2C

    CH2 H2C

    O

    H3C CH2

    H2C

    CH2 H2C

    CH2 H2C

    O

    H3C CH2

    H2C

    CH2 H2C

    CH2 H2C

    O H 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.

    CH3 O

    H

    H3C CH2

    CH2 CH2

    CH2 CH2

    CH2 O

    H

    Nonpolar, or hydrophobic portions

    of molecules Polar, or hydrophilic portions of molecules

    Physical Properties of Alcohols

  • Physical Properties of Alcohols-Solubility

  • Physical Properties of Alcohols-Solubility

    CH3 O

    H

    CH3 O

    H H

    O H

    THE RELATIVELY SMALL ATTRACTION BETWEEN METHANOL MOLECULES MAKES IT EASY FOR WATER TO SEPARATE INDIVIDUAL METHANOL

    MOLECULES FROM EACH OTHER AND DISSOLVE THE ALCOHOL.

    METHANOL IS VERY SOLUBLE IN WATER.

    H3C CH2

    CH2 CH2

    CH2 CH2

    CH2 O

    H

    H3C CH2

    CH2 CH2

    CH2 CH2

    CH2 O

    H H

    O 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 Phenols Acidity

  • ClH Cl

    H3C C

    O

    O

    H H3C C

    O

    O

    Ar O H

    Ar O

    Alkyl O H

    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 CH2 O H

    Na

    H3C CH2 O H

    Na

    H3C CH2 O H

    Na

    H3C CH2 O H

    Na

    H3C CH2 O

    Na + H22

    H3C CH2 O H

    Na

    H3C CH2 O H

    Na

    H3C CH2 O H

    Na

    H3C CH2 O H

    Na

    H3C CH2 O

    Na + H22

    H3C CH2 O H

    Na

    H3C CH2 O H

    Na

    H3C CH2 O H

    Na

    H3C CH2 O H

    Na

    H3C CH2 O

    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

    CH3 2-nitrophenol

    or ortho-nitrophenol

    3-chlorophenol or

    meta-chlorophenol

    4-methylphenol or

    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 Solids Soluble in Nonpolar Solvents Also, 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

    Cl OH

    CH3

    OH

    N O O

    OH

    O

    CH3

    OH

    N O O

    N

    O

    O

    OH OH

    N O O

    N

    O

    O N

    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-Base Reactions

    Phenol Sodium phenoxide

    Hydroquinone Paraquinone

    Oxidation- Reduction Reactions

  • 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