(20) session 20 alcohols & phenols

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4/26/2012 1 Session 20 Organic Chemistry, UNAM School of Medicine 1 Alcohols & Phenols ( Alcohols & Phenols ( Alcohols & Phenols ( Alcohols & Phenols (Hydroxybenzenes Hydroxybenzenes Hydroxybenzenes Hydroxybenzenes) 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

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

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� 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

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

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� 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??

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� 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

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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

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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

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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

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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”

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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

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Structure of alcoholsStructure of alcoholsStructure of alcoholsStructure of alcohols

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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:

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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:

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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)…cont’d

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

� Examples:

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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)…cont’d

- Cyclic alcohols: Named using the prefix “cyclo-”

-The OH group is assumed to be on C 1

� Examples:

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1-ethylcyclopropanol

5-amino-3-methyl-cycloheptanol

Nomenclature of phenolsNomenclature of phenolsNomenclature of phenolsNomenclature of phenols

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

• Examples:

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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 120°C

� Unusually high boiling points of alcohols - due to H bonding

between alcohol molecules

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vs.

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

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� 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

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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

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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 solubility decreases as the alkyl group becomes larger

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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+

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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 acids

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

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

(ArO−−−−)

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

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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

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

due to resonance stabilisation of the phenoxide ion

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Quiz: Alcohols & Phenols

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� Give a systematic (IUPAC) name & indicate if it is 1°, 2° or 3° alcohol:

1. H

� Draw line-bond structures for the following names:

3. 3-cyclohexen-1-ol

� Data for isomeric 4-carbon alcohols show that there is a decrease in boiling point with increasing substitution of the OH-bearing carbon. Explain why?

5. 1-butanol, bp. 117.5 °C2-butanol , bp. 99.5 °C2-methyl-2-propanol, bp. 82.2 °C

2.

4. 1,4-pentanediol

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Thank you

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END

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� Quiz answers:

1. 4-methylcyclohexanol (2° alcohol)

2. 5-chloro-2-methyl-pentan-2-ol (3° alcohol)

3. H

4. H

5. Next slide…

3-cyclohexen-1-ol/cyclohex-3-en-1-ol

1,4-pentanediol/pentane-1,4-diol

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� Quiz answers:

5. In general, the boiling point of a series of isomers decrease with branching.

The more nearly spherical a compound becomes, the less surface area it has

relative to a straight chain compound of the same molecular weight and

functional group type. A smaller surface area allows fewer Van der Waals

interactions. In addition, branching in alcohols makes it more difficult for

hydroxyl groups to approach each other to form hydrogen bonds. A given

volume of 2-methyl-2-propanol therefore contains fewer hydrogen bonds

than the same volume of 1-butanol, and less energy is needed to break

them in boiling.

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