(20) session 20 alcohols & phenols

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Transcript of (20) session 20 alcohols & phenols

  • 4/26/2012

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    Session 20

    Organic Chemistry, UNAM School of Medicine1

    Alcohols & Phenols (Alcohols & Phenols (Alcohols & Phenols (Alcohols & Phenols (HydroxybenzenesHydroxybenzenesHydroxybenzenesHydroxybenzenes))))

    Dr L.H.A. Prins (Ph.D.)

    Dept. of Pharmacy

    UNAM

    Learning Outcomes

    2

    By the end of this session, the student should be able to:

    Understand the importance of alcohols & phenols

    Describe the structure of alcohols & phenols

    Name alcohols & phenols according to IUPAC system

    Describe the physical properties of alcohols & phenols

    Organic Chemistry, UNAM School of Medicine

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    Importance: Alcohols??Importance: Alcohols??Importance: Alcohols??Importance: Alcohols??

    3 Organic Chemistry, UNAM School of Medicine

    Ethanol (ethyl alcohol, CH3CH2OH): Most widely known alcohol

    Applications: In alcoholic beverages, As a solvent, and Added to petrol to aid combustion efficiency

    Methanol (methyl alcohol, CH3OH): Important industrial chemical

    Applications: As a solvent, and As a starting material for production of formaldehyde (CH20) & acetic acid (CH3CO2H)

    Importance: Alcohols??Importance: Alcohols??Importance: Alcohols??Importance: Alcohols??

    4 Organic Chemistry, UNAM School of Medicine

    Propan-2-ol/2-propanol (isopropyl alcohol, CH3CH3CHOH):

    Known as rubbing alcohol

    Applications:

    Used as a skin cleanser for injections

    and minor cuts

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    Importance: Phenols??Importance: Phenols??Importance: Phenols??Importance: Phenols??

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    Phenols: Ingredients in cloves, vanillia, nutmeg, mint

    Organic Chemistry, UNAM School of Medicine

    Importance: Phenols??Importance: Phenols??Importance: Phenols??Importance: Phenols??

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    Methyl salicylate: Found in oil of wintergreen

    Many phenols are used as disinfectants & antiseptics

    Organic Chemistry, UNAM School of Medicine

    OH

    OH

    OH

    OH

    OH

    phenol(hydroxybenzene)

    resorcinol (3-hydroxyphenol) 4-hexylresorcinol

    (4-hexyl-3-hydroxyphenol)

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    Importance: Importance: Importance: Importance: Phenols??Phenols??Phenols??Phenols??

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    trans-Resveratrol: - Naturally occurring phenol

    - Currently - numerous animal & human studies into its effects: Anti-cancer, anti-inflammatory, blood-sugar-lowering & other

    beneficial cardiovascular effects have been reported

    Effect on lifespan is still uncertain

    Organic Chemistry, UNAM School of Medicine

    Structure of alcoholsStructure of alcoholsStructure of alcoholsStructure of alcohols

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    Aliphatic alcohols: Contain an OH group connected to an alkyl, alkenyl or alkynal group Structure of alkanol/alkyl alcohol resembles structure of H2O, with

    an alkyl group replacing one of the H atoms of H2O Both H2O & methanol have sp

    3 hybridised O atoms

    Organic Chemistry, UNAM School of Medicine

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    Structure of phenolsStructure of phenolsStructure of phenolsStructure of phenols

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    Aromatic alcohols/phenols: Contain an OH group connected to a C in a benzene ring O is sp3 hybridised & the aryl/aromatic C is sp2 hybridised

    Phenol is from phenyl alcohol

    Organic Chemistry, UNAM School of Medicine

    Structure of alcoholsStructure of alcoholsStructure of alcoholsStructure of alcohols

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    Classification of aliphatic alcohols:

    Primary (1o):OH attached to 1o carbon - RCH2-OH

    Secondary (2o):OH attached to 2o carbon - R2CH-OH

    Tertiary (3o):OH attached to 3o carbon - R3C-OH

    Remember: Look at the # of organic groups (R) bonded to OH-

    bearing C

    Organic Chemistry, UNAM School of Medicine

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    Structure of alcoholsStructure of alcoholsStructure of alcoholsStructure of alcohols

    11 Organic Chemistry, UNAM School of Medicine

    Nomenclature of aliphatic alcoholsNomenclature of aliphatic alcoholsNomenclature of aliphatic alcoholsNomenclature of aliphatic alcohols

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    Common names - name of alkyl group to which OH group is attached, followed by the word alcohol

    Examples:

    Organic Chemistry, UNAM School of Medicine

    ethyl alcohol propyl alcohol isopropyl alcohol neopentyl alcohol

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    Nomenclature of aliphatic alcoholsNomenclature of aliphatic alcoholsNomenclature of aliphatic alcoholsNomenclature of aliphatic alcohols

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    Systematic names (IUPAC) - obtained by replacing the e at the end of the name of the parent hydrocarbon with the suffix ol

    Remember: Alkanol

    Examples:

    Organic Chemistry, UNAM School of Medicine

    ethanol propanol propan-2-ol/2-propanol

    2,2-dimethylpropanol

    Nomenclature of aliphatic alcoholsNomenclature of aliphatic alcoholsNomenclature of aliphatic alcoholsNomenclature of aliphatic alcohols

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    Systematic names (IUPAC)contd

    - If OH group is classified as substituent (side-chain) in a compound called a hydroxy group

    Examples:

    Organic Chemistry, UNAM School of Medicine

    4-hydroxybutanoic acid 4-hydroxybutanal

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    Nomenclature of aliphatic alcoholsNomenclature of aliphatic alcoholsNomenclature of aliphatic alcoholsNomenclature of aliphatic alcohols

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    Systematic names (IUPAC)contd

    - Cyclic alcohols: Named using the prefix cyclo-

    -The OH group is assumed to be on C 1

    Examples:

    Organic Chemistry, UNAM School of Medicine

    1-ethylcyclopropanol

    5-amino-3-methyl-cycloheptanol

    Nomenclature of phenolsNomenclature of phenolsNomenclature of phenolsNomenclature of phenols

    16

    Phenols:Named as described previously for aromatic compounds (Session 18) Note that -phenol is used as the parent name rather than -benzeneName substituents on aromatic ring by their position from OH (C attached to OH is always carbon # 1)

    Examples:

    Organic Chemistry, UNAM School of Medicine

    3-methylphenol(m-methylphenol) 2,4-dinitrophenol

    OH

    NO2

    NO2

    OH

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    Physical properties of alcohols Physical properties of alcohols Physical properties of alcohols Physical properties of alcohols

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    Boiling points:

    Ethanol & propane have similar molecular weights, yet their boiling

    points differ by about 120C

    Unusually high boiling points of alcohols - due to H bonding

    between alcohol molecules

    Organic Chemistry, UNAM School of Medicine

    vs.

    Physical properties of alcohols Physical properties of alcohols Physical properties of alcohols Physical properties of alcohols

    18

    Boiling points:

    Hydroxyl (OH) hydrogen of ethanol is strongly polarised by its bond

    to O ( EN), Forms a H bond with a pair of non-bonding e- from O atom of

    another alcohol molecule

    Organic Chemistry, UNAM School of Medicine

    H-bonds: Only with H attached to N, O or F

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    Physical properties of alcohols Physical properties of alcohols Physical properties of alcohols Physical properties of alcohols

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    H2O solubility:

    H2O & alcohols have similar properties because, they all contain OH

    groups that can form H bonds

    Alcohols form H bonds with H2O & several lower-molecular-weight

    alcohols are miscible (soluble in any proportions) with H2O

    OH group = hydrophilic (water loving) because of its affinity for H2O & other polar substances

    Alkyl group = hydrophobic (water hating) because it disrupts the network of H bonds & dipole-dipole attractions of a

    polar solvent such as H2O

    Organic Chemistry, UNAM School of Medicine

    Physical properties of alcohols Physical properties of alcohols Physical properties of alcohols Physical properties of alcohols

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    H2O solubility:

    H2O solubility decreases as the alkyl group becomes larger

    Organic Chemistry, UNAM School of Medicine

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    Physical properties of alcohols Physical properties of alcohols Physical properties of alcohols Physical properties of alcohols

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    Acidity & basicity:Alcohols & phenols are weak acids & bases Alcohols are weak Bronsted bases

    Protonated by strong acids to yield oxonium ions, ROH2+

    Organic Chemistry, UNAM School of Medicine

    Physical properties of alcohols Physical properties of alcohols Physical properties of alcohols Physical properties of alcohols

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    Acidity & basicity:Alcohols & phenols are weak acids & bases Alcohols are weak Bronsted acids

    Can transfer a H+ to H2O to a very small extent

    Produces H3O+ & an alkoxide ion (RO), or a phenoxide ion

    (ArO)

    Organic Chemistry, UNAM School of Medicine

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    Physical properties of alcohols Physical properties of alcohols Physical properties of alcohols Physical properties of alcohols

    23 Organic Chemistry, UNAM School of Medicine

    Physical properties of alcohols Physical properties of alcohols Physical properties of alcohols Physical properties of alcohols

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    Acidity & basicity:Alcohols & phenols are weak acids & bases

    Phenols (pKa ~10) are much more acidic than alcohols (pKa ~ 16)

    due to resonance stabilisation of the phenoxide ion

    Organic Chemistry, UNAM School of Medicine

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    Quiz: Alcohols & Phenols

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    Give a systematic (IUPAC) name & indicate if