Textbook Question
(b) Explain why m-xylene undergoes nitration 100 times faster than p-xylene.
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Ch. 17 - Reactions of Aromatic Compounds
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 17, Problem 9
When bromine is added to two beakers, one containing phenyl isopropyl ether and the other containing cyclohexene, the bromine color in both beakers disappears. What observation could you make while performing this test that would allow you to distinguish the alkene from the aryl ether?
Verified step by step guidance1
Step 1: Understand the reactivity of bromine with alkenes and aryl ethers. Bromine reacts with alkenes through an electrophilic addition reaction, leading to the formation of a dibromo product. Aryl ethers, on the other hand, do not undergo this reaction under normal conditions but may react through a different mechanism, such as substitution, if activated.
Step 2: Recognize the visual cue in the reaction with cyclohexene. When bromine reacts with cyclohexene, the bromine color (reddish-brown) disappears due to the formation of a colorless dibromo product. This reaction is rapid and occurs at room temperature.
Step 3: Consider the reaction with phenyl isopropyl ether. The disappearance of bromine color in this case is likely due to a slower reaction, such as bromination at the aromatic ring (electrophilic aromatic substitution), which may require specific conditions like a catalyst or heat.
Step 4: Observe the reaction rate. The reaction with cyclohexene (alkene) is much faster compared to the reaction with phenyl isopropyl ether (aryl ether). This difference in reaction rate can help distinguish the two compounds.
Step 5: Confirm the product formation. To further distinguish the two, you could analyze the reaction products. Cyclohexene will form a dibromoalkane, while phenyl isopropyl ether may form a brominated aromatic compound. This can be confirmed using techniques like NMR or IR spectroscopy.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Electrophilic Addition Reactions
Electrophilic addition reactions occur when an electrophile reacts with a nucleophile, leading to the formation of a more saturated compound. In the case of alkenes, such as cyclohexene, bromine adds across the double bond, resulting in the disappearance of the bromine color due to the formation of a dibromide. This reaction is characteristic of alkenes and can be used to distinguish them from other compounds.
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Features of Addition Mechanisms.
Aromatic Compounds
Aromatic compounds, like phenyl isopropyl ether, contain a stable ring structure with delocalized π electrons, which makes them less reactive towards electrophiles compared to alkenes. When bromine is added to an aryl ether, there is typically no reaction under normal conditions, and the bromine color remains. This stability is a key feature that can help differentiate aromatic compounds from alkenes.
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Color Change as an Indicator
The disappearance of bromine's reddish-brown color is a visual indicator of a chemical reaction occurring. In the context of this experiment, if the color disappears in the beaker with cyclohexene, it indicates that bromine has reacted with the alkene. Conversely, if the color persists in the beaker with phenyl isopropyl ether, it suggests that no reaction has taken place, allowing for differentiation between the two substances.
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Related Practice
Textbook Question
Styrene (vinylbenzene) undergoes electrophilic aromatic substitution much faster than benzene, and the products are found to be primarily ortho- and para-substituted styrenes. Use resonance forms of the intermediates to explain these results.
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Textbook Question
Propose a mechanism for the bromination of ethoxybenzene to give o- and p-bromoethoxybenzene.
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Textbook Question
Predict the mononitration products of the following compounds.
d. p-methoxybenzoic acid
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Textbook Question
In an aqueous solution containing sodium bicarbonate, aniline reacts quickly with bromine to give 2,4,6-tribromoaniline. Nitration of aniline requires very strong conditions, however, and the yields (mostly m-nitroaniline) are poor.
c. Although nitration of aniline is slow and gives mostly meta substitution, nitration of acetanilide (PhNHCOCH3) goes quickly and gives mostly para substitution. Use resonance forms to explain this difference in reactivity.
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Textbook Question
Predict the mononitration products of the following compounds.
a. o-nitrotoluene
b. m-chlorotoluene
c. o-bromobenzoic acid
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