Textbook Question
Propose mechanisms for the following reactions.
(a)
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Ch. 7 - Structure and Synthesis of Alkenes; Elimination
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 7, Problem 34d
Propose mechanisms for the following reactions.
(d) 
Verified step by step guidance1
Step 1: Protonation of the alcohol group occurs in the presence of H2SO4, converting the hydroxyl group (-OH) into a better leaving group (water). This step is facilitated by the acidic environment.
Step 2: The protonated alcohol group leaves, forming a carbocation intermediate. The carbocation is stabilized by resonance or hyperconjugation, depending on the structure of the molecule.
Step 3: A hydride shift or alkyl shift may occur to form a more stable carbocation. This rearrangement is driven by the molecule's tendency to achieve greater stability.
Step 4: Intramolecular cyclization occurs as the carbocation reacts with a nearby double bond, forming a new ring structure. This step is key to forming the minor product.
Step 5: Deprotonation of the newly formed ring structure occurs, resulting in the formation of the minor product with a double bond in the ring system. This step restores neutrality to the molecule.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acid-Catalyzed Dehydration
Acid-catalyzed dehydration is a reaction where an alcohol is converted into an alkene through the removal of water, facilitated by an acid. In this case, sulfuric acid (H2SO4) acts as a catalyst, promoting the formation of a carbocation intermediate, which can then lose a proton to form a double bond. This mechanism is crucial for understanding how the starting alcohol can rearrange to form different products.
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General features of acid-catalyzed dehydration.
Carbocation Stability
Carbocation stability is a key concept in organic chemistry that refers to the relative stability of positively charged carbon species. Tertiary carbocations are more stable than secondary or primary ones due to hyperconjugation and inductive effects from surrounding alkyl groups. Understanding carbocation stability helps predict the major and minor products of reactions, as more stable carbocations are more likely to form during the reaction.
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Rearrangement Reactions
Rearrangement reactions involve the structural reorganization of a molecule to form a more stable product. In the context of dehydration reactions, carbocations can undergo rearrangement to form more stable structures, which can lead to the formation of unexpected minor products. Recognizing potential rearrangements is essential for predicting the outcome of reactions and understanding the diversity of organic compounds that can be synthesized.
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Related Practice
Textbook Question
Show the product(s) you expect from dehydration of the following alcohols when they are heated in sulfuric or phosphoric acid. In each case, use a mechanism to show how the products are formed.
(b)
977
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Textbook Question
Show the product(s) you expect from dehydration of the following alcohols when they are heated in sulfuric or phosphoric acid. In each case, use a mechanism to show how the products are formed.
(c)
697
views
Textbook Question
Propose mechanisms for the following reactions.
(c)
2434
views
Textbook Question
Propose mechanisms for the following reactions.
(b)
3085
views
Textbook Question
Show the product(s) you expect from dehydration of the following alcohols when they are heated in sulfuric or phosphoric acid. In each case, use a mechanism to show how the products are formed.
(a)
2172
views