Domanda del libro di testo
(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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TOC.tableOfContents
- 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
Capitolo 17, Problema 2
Propose a mechanism for the aluminum chloride–catalyzed reaction of benzene with chlorine.
Guida verificata passo dopo passo1
The reaction is an example of an electrophilic aromatic substitution (EAS) reaction. Begin by recognizing that aluminum chloride (AlCl₃) acts as a Lewis acid catalyst, which helps to generate the electrophile (Cl⁺) from molecular chlorine (Cl₂).
In the first step, AlCl₃ interacts with Cl₂ to form a complex: \( \text{Cl}_2 + \text{AlCl}_3 \rightarrow \text{Cl}^+ + \text{AlCl}_4^- \). This generates the highly reactive electrophile, \( \text{Cl}^+ \).
Next, the benzene ring, which is electron-rich due to its delocalized π-electrons, attacks the \( \text{Cl}^+ \) electrophile. This forms a sigma complex (also called an arenium ion), where one of the benzene carbons is bonded to the chlorine atom, and the aromaticity of the ring is temporarily lost.
In the subsequent step, the sigma complex loses a proton (H⁺) from the carbon bonded to the chlorine atom. This proton is abstracted by \( \text{AlCl}_4^- \), regenerating \( \text{AlCl}_3 \) and forming HCl as a byproduct. The aromaticity of the benzene ring is restored in this step.
Finally, the overall reaction results in the formation of chlorobenzene (C₆H₅Cl) and HCl, with \( \text{AlCl}_3 \) acting as a catalyst and being regenerated at the end of the reaction.
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Electrophilic Aromatic Substitution
Electrophilic aromatic substitution (EAS) is a fundamental reaction in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. In this mechanism, the aromatic system donates electrons to the electrophile, forming a sigma complex. This process is crucial for understanding how benzene reacts with various electrophiles, including chlorine in the presence of a catalyst like aluminum chloride.
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03:07
EAS Review
Role of Aluminum Chloride as a Catalyst
Aluminum chloride (AlCl3) acts as a Lewis acid catalyst in the reaction between benzene and chlorine. It enhances the electrophilicity of chlorine by forming a complex with it, which generates a more reactive electrophile, Cl+. This activation is essential for facilitating the EAS mechanism, allowing the chlorine to effectively attack the benzene ring.
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Percorso guidato
2:10Introduction to Catalysis Concept 1
Formation of the Sigma Complex
The sigma complex, or arenium ion, is an intermediate formed during the electrophilic aromatic substitution process. When the electrophile attacks the benzene ring, it disrupts the aromaticity, leading to a positively charged intermediate. This step is critical as it determines the stability of the reaction pathway and influences the final product formation after deprotonation.
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05:02Coordination Complexes
Pratica correlata
Domanda del libro di testo
Step 2 of the iodination of benzene shows water acting as a base and removing a proton from the sigma complex. We did not consider the possibility of water acting as a nucleophile and attacking the carbocation, as in an electrophilic addition to an alkene. Draw the reaction that would occur if water reacted as a nucleophile and added to the carbocation. Explain why this type of addition is rarely observed.
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Domanda del libro di testo
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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Domanda del libro di testo
p-Xylene undergoes nitration much faster than benzene. Use resonance forms of the sigma complex to explain this accelerated rate
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