(20) session 20 alcohols & phenols
-
Upload
nixon-hamutumwa -
Category
Healthcare
-
view
23 -
download
1
Transcript of (20) session 20 alcohols & phenols
4/26/2012
1
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
4/26/2012
2
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
4/26/2012
3
Importance: Phenols??Importance: Phenols??Importance: Phenols??Importance: Phenols??
5
� Phenols: Ingredients in cloves, vanillia, nutmeg, mint
Organic Chemistry, UNAM School of Medicine
Importance: Phenols??Importance: Phenols??Importance: Phenols??Importance: Phenols??
6
� 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)
4/26/2012
4
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
Organic Chemistry, UNAM School of Medicine
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 sp
3 hybridised O atoms
Organic Chemistry, UNAM School of Medicine
4/26/2012
5
Structure of phenolsStructure of phenolsStructure of phenolsStructure of phenols
9
� 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
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
Organic Chemistry, UNAM School of Medicine
4/26/2012
6
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
12
� 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
4/26/2012
7
Nomenclature of aliphatic alcoholsNomenclature of aliphatic alcoholsNomenclature of aliphatic alcoholsNomenclature of aliphatic alcohols
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:
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
14
� Systematic names (IUPAC)…cont’d
- 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
4/26/2012
8
Nomenclature of aliphatic alcoholsNomenclature of aliphatic alcoholsNomenclature of aliphatic alcoholsNomenclature of aliphatic alcohols
15
� Systematic names (IUPAC)…cont’d
- 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 “-benzene”Name 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
4/26/2012
9
Physical properties of alcohols Physical properties of alcohols Physical properties of alcohols Physical 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
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
4/26/2012
10
Physical properties of alcohols Physical properties of alcohols Physical properties of alcohols Physical properties of alcohols
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
Organic Chemistry, UNAM School of Medicine
Physical properties of alcohols Physical properties of alcohols Physical properties of alcohols Physical properties of alcohols
20
� H2O solubility:
� H2O solubility decreases as the alkyl group becomes larger
Organic Chemistry, UNAM School of Medicine
4/26/2012
11
Physical properties of alcohols Physical properties of alcohols Physical properties of alcohols Physical properties of alcohols
21
� 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
22
� 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
4/26/2012
12
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
24
� 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
4/26/2012
13
Quiz: Alcohols & Phenols
25
� 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
Organic Chemistry, UNAM School of Medicine
Thank you
26
END
Organic Chemistry, UNAM School of Medicine
4/26/2012
14
27
� 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
Organic Chemistry, UNAM School of Medicine
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 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.
Organic Chemistry, UNAM School of Medicine