p 34 Aromatic Compounds
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Transcript of p 34 Aromatic Compounds
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AROMATIC COMPOUNDS Prepared by: AGLS
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Aromatic compounds represent another example of unsaturated hydrocarbons.
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Tamoxifen, a potent anticancer drug sold
under the trade name of Novaldex, contains three benzene rings.
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The physical properties of aromatic hydrocarbons are similar to other hydrocarbons—they have low melting points and boiling
points and are water insoluble.
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Nomenclature of Benzene Derivatives
Monosubstituted Benzenes • To name a benzene ring with one substituent, name the
substituent and add the word benzene. • Carbon substituents are named as alkyl groups. When a
halogen is a substituent, name the halogen by changing the -ine ending of the name of the halogen to the suffix -o;
for example, chlorine → chloro.
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Many monosubstituted benzenes, such as those with methyl (CH3–), hydroxyl (–OH), and amino (–NH2) groups, have common names.
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DISUBSTITUTED BENZENES • There are three different ways that two groups can be attached to a benzene ring,
so a prefix— ortho, meta, or para—is used to designate the relative position of the two substituents.
• Ortho, meta, and para are generally abbreviated as o, m, and p, respectively.
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If the two groups on the benzene ring are different, alphabetize the name of the substituents preceding the word benzene. If one of the substituents is part of a common root, name the molecule as a derivative of that monosubstituted benzene.
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POLYSUBSTITUTED BENZENES For three or more substituents on a benzene ring:
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EXAMPLES
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SAMPLE PROBLEM p.35
Name each of the following aromatic compounds.
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Solution
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PROBLEM 1
Give the IUPAC name of each compound.
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PROBLEM 2
Draw the structure corresponding to each name. a) pentylbenzene b) o-dichlorobenzene c) m-bromoaniline d) 4-chloro-1,2-diethylbenzene
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SPECIAL TOPIC
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SUNSCREENS AND ANTIOXIDANTS Sunscreens
• All commercially available sunscreens contain a benzene ring. • A sunscreen absorbs ultraviolet radiation and thus shields the
skin for a time from its harmful effects. • Two sunscreens that have been used for this purpose are p-
aminobenzoic acid (PABA) and Padimate O.
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Commercial sunscreens
are given an SPF rating
(sun protection factor),
according to the amount
of sunscreen present.
The higher the number,
the greater the
protection.
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PROBLEM 1 Identify the functional groups in each sunscreen: (a) PABA; (b) Padimate O.
PROBLEM 2
Which of the following compounds might be an ingredient in a commercial sunscreen? Explain why or why not.
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Phenols as Antioxidants • Vanillin from the vanilla bean is a phenol, as is curcumin,
a yellow pigment isolated from turmeric, a tropical perennial in the ginger family and a principal ingredient in curry powder.
• Curcumin has long been used as an anti-inflammatory agent in traditional eastern medicine.
• In some preliminary research carried out with mice, curcumin was shown to correct the defect that causes cystic fibrosis, a fatal genetic disease that afflicts 30,000 children and young adults in the United States.
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Phenols as Antioxidants Many phenols are antioxidants, compounds that prevent unwanted oxidation reactions from occurring. Two examples are naturally occurring vitamin E and synthetic BHT. The OH group on the benzene ring is the key functional group that prevents oxidation reactions from taking place.
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Vitamin E • Vitamin E is a natural antioxidant found in fish oil, peanut
oil, wheat germ, and leafy greens. • Although the molecular details of its function remain
obscure, it is thought that vitamin E prevents the unwanted oxidation of unsaturated fatty acid residues in cell membranes.
• vitamin E helps retard the aging process. • Synthetic antioxidants such as BHT—butylated hydroxy
toluene—are added to packaged and prepared foods to prevent oxidation and spoilage.
• BHT is a common additive in breakfast cereals
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EXAMPLES
purported health benefits of antioxidants
have made them a popular component
in anti-aging formulations.
Nuts are an excellent source of vitamin E.
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PROBLEM 3
Which of the following compounds might be antioxidants?