Textbook Question
Show how you would use the Friedel–Crafts acylation, Clemmensen reduction, and/or Gatterman–Koch synthesis to prepare the following compounds:
f. 1-phenyl-2,2-dimethylpropane
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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 22
Propose a mechanism that shows why p-chlorotoluene reacts with sodium hydroxide at 350 °C to give a mixture of p-cresol and m-cresol.
Verified step by step guidance1
Step 1: Recognize that the reaction involves nucleophilic aromatic substitution (NAS). This type of reaction occurs when an electron-withdrawing group (such as a halogen) is present on an aromatic ring, making the ring susceptible to attack by a nucleophile (in this case, hydroxide ion, OH⁻).
Step 2: Identify the electron-withdrawing group and its position. In p-chlorotoluene, the chlorine atom is the electron-withdrawing group, and it is located at the para position relative to the methyl group. The methyl group is electron-donating, which slightly affects the reactivity of the ring.
Step 3: Explain the role of high temperature (350 °C). The elevated temperature provides the energy required for the reaction to proceed via the benzyne intermediate mechanism, which is common in NAS reactions under harsh conditions. This mechanism involves elimination followed by addition.
Step 4: Describe the formation of the benzyne intermediate. The hydroxide ion first abstracts a proton from the position ortho to the chlorine atom, leading to the elimination of the chlorine atom and the formation of a triple bond (benzyne intermediate) in the aromatic ring. This intermediate is highly reactive.
Step 5: Explain the nucleophilic attack on the benzyne intermediate. The hydroxide ion can attack either end of the triple bond in the benzyne intermediate, leading to the formation of two possible products: p-cresol (if the attack occurs at the original para position) and m-cresol (if the attack occurs at the meta position). This accounts for the mixture of products observed in the reaction.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Nucleophilic Aromatic Substitution
Nucleophilic aromatic substitution (NAS) is a reaction mechanism where a nucleophile replaces a leaving group on an aromatic ring. In the case of p-chlorotoluene, the chlorine atom is a good leaving group, allowing sodium hydroxide (a strong nucleophile) to attack the aromatic ring. This mechanism is crucial for understanding how the reaction proceeds to form p-cresol and m-cresol.
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Regioselectivity
Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others. In the reaction of p-chlorotoluene with sodium hydroxide, the formation of p-cresol and m-cresol illustrates regioselectivity, as the nucleophile can attack at different positions on the aromatic ring. The electronic effects and steric factors influence which isomer is predominantly formed.
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Thermal Conditions and Reaction Kinetics
The temperature of a reaction can significantly affect its kinetics and the products formed. At elevated temperatures, such as 350 °C, the reaction may favor certain pathways or mechanisms, enhancing the likelihood of NAS occurring. Understanding how temperature influences reaction rates and equilibria is essential for predicting the outcome of the reaction between p-chlorotoluene and sodium hydroxide.
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Related Practice
Textbook Question
Propose mechanisms and show the expected products of the following reactions.
(a) 2,4-dinitrochlorobenzene + sodium methoxide (NaOCH3)
(b) 2,4-dimethylchlorobenzene + sodium hydroxide, 350 °C
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Textbook Question
The highly reactive triple bond of benzyne is a powerful dienophile. Predict the product of the Diels–Alder reaction of benzyne (from chlorobenzene and NaOH, heated) with cyclopentadiene.
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Textbook Question
Show how you would use the Friedel–Crafts acylation, Clemmensen reduction, and/or Gatterman–Koch synthesis to prepare the following compounds:
g. n-butylbenzene
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Textbook Question
Propose mechanisms and show the expected products of the following reactions.
(c) p-nitrobromobenzene + methylamine (CH3–NH2)
(d) 2,4-dinitrochlorobenzene + excess hydrazine (H2N–NH2)
Textbook Question
Show how you would use the Friedel–Crafts acylation, Clemmensen reduction, and/or Gatterman–Koch synthesis to prepare the following compounds:
h.
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