Textbook Question
Write a balanced equation for each reaction, showing the major product you expect.
(a)
3
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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 52a,b
Predict the major products of acid-catalyzed dehydration of the following alcohols.
(a) 
(b) 
Verified step by step guidance1
Step 1: Understand the reaction mechanism. Acid-catalyzed dehydration of alcohols involves the removal of a water molecule to form an alkene. This reaction proceeds via an E1 mechanism for secondary and tertiary alcohols, where the alcohol is protonated to form a good leaving group (water), followed by carbocation formation and elimination.
Step 2: Analyze the structure of pentan-2-ol (a). Protonation of the hydroxyl group (-OH) occurs first, forming a good leaving group (water). The departure of water leads to the formation of a secondary carbocation at the second carbon. Consider carbocation rearrangement if it leads to a more stable carbocation, but in this case, the secondary carbocation is stable enough.
Step 3: Determine the major product for pentan-2-ol (a). The elimination step involves the removal of a proton from a β-carbon (adjacent to the carbocation) to form the double bond. Apply Zaitsev's rule, which states that the more substituted alkene is the major product. The double bond will likely form between the second and third carbons, resulting in the major product.
Step 4: Analyze the structure of 1-methylcyclopentanol (b). Protonation of the hydroxyl group (-OH) occurs first, forming a good leaving group (water). The departure of water leads to the formation of a tertiary carbocation at the carbon bearing the methyl group. Tertiary carbocations are highly stable, so no rearrangement is needed.
Step 5: Determine the major product for 1-methylcyclopentanol (b). The elimination step involves the removal of a proton from a β-carbon to form the double bond. Apply Zaitsev's rule again, favoring the formation of the more substituted alkene. The double bond will likely form between the carbon bearing the methyl group and one of the adjacent carbons in the cyclopentane ring, resulting in the major product.
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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 a water molecule, facilitated by an acid. The process typically involves protonation of the alcohol's hydroxyl group, making it a better leaving group, followed by the formation of a carbocation intermediate. This reaction is crucial in organic synthesis for producing alkenes from alcohols.
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06:01
General features of acid-catalyzed dehydration.
Carbocation Stability
Carbocation stability is a key factor in determining the outcome of dehydration reactions. Carbocations are positively charged species that can vary in stability based on their structure; tertiary carbocations are more stable than secondary, which are more stable than primary. The stability influences the likelihood of forming certain products during the dehydration process, as more stable carbocations are favored.
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05:58Determining Carbocation Stability
Zaitsev's Rule
Zaitsev's Rule states that in elimination reactions, the more substituted alkene is typically the major product. This principle applies to acid-catalyzed dehydration, where the elimination of water leads to the formation of alkenes. Understanding this rule helps predict the major product when multiple elimination pathways are possible, guiding the synthesis of desired compounds.
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Related Practice
Textbook Question
Predict the major products of acid-catalyzed dehydration of the following alcohols.
(c)
(d)
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Textbook Question
Predict the products of the following reactions. When more than one product is expected, predict which will be the major product.
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Textbook Question
What halides would undergo E2 dehydrohalogenation to give the following pure alkenes?
d. methylenecyclohexane
1
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Textbook Question
What halides would undergo E2 dehydrohalogenation to give the following pure alkenes?
e. 4-methylcyclohexene
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Textbook Question
What halides would undergo E2 dehydrohalogenation to give the following pure alkenes?
a. hex-1-ene
b. isobutylene
c. pent-2-ene
4
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