(20) session 20 alcohols & phenols

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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??
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??
5
Phenols: Ingredients in cloves, vanillia, nutmeg, mint
Importance: Phenols??Importance: Phenols??Importance: Phenols??Importance: Phenols??
6
Methyl salicylate:
Found in
oil of wintergreen
Many phenols are used as disinfectants & antiseptics
O H
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??
7
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
Structure of alcoholsStructure of alcoholsStructure of alcoholsStructure of alcohols
8
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 sp3 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”
10
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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Nomenclature of aliphatic alcoholsNomenclature of aliphatic alcoholsNomenclature of aliphatic alcoholsNomenclature of aliphatic alcohols
12
Common names - name of alkyl group to which OH group is
attached, followed by the word “alcohol”
Examples:
ethyl alcohol propyl alcohol isopropyl alcohol neopentyl alcohol

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13
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:
ethanol propanol propan-2-ol/
2-propanol
2,2-
dimethylpropanol
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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:
4-hydroxybutanoic acid 4-hydroxybutanal

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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:
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
“-benzene”
Name substituents on aromatic ring by their position from OH (C
attached to OH is always carbon # 1)
•Examples:
3-methylphenol
(m-methylphenol) 2,4-dinitrophenol
O H
NO2
NO2
OH

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Physical properties of alcoholsPhysical properties of alcoholsPhysical properties of alcoholsPhysical properties of alcohols
17
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
vs.
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
H-bonds: Only with H attached
to N, O or F

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19
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
20
H2O solubility:
H2O solubility decreases as the alkyl group becomes larger

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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
+
22
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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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 °C
2-butanol , bp. 99.5 °C
2-methyl-2-propanol, bp. 82.2 °C
2.
4. 1,4-pentanediol
Thank you
26
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
28
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 fewerVan derWaals
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.

(20) session 20 alcohols & phenols

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