Textbook Question
In the presence of a small amount of bromine, cyclohexene undergoes the following light-promoted reaction:
d. Explain why cyclohexene reacts with bromine much faster than cyclohexane, which must be heated to react.
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Ch.6 - Alkyl Halides; Nucleophilic Substitution
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 6, Problem 26b
Propose a mechanism involving a hydride shift or an alkyl shift for each solvolysis reaction. Explain how each rearrangement forms a more stable intermediate.
Hint: Most rearrangements convert 2° (or incipient 1°) carbocations to 3° or resonance-stabilized carbocations. ![]()
(b) 
Verified step by step guidance1
Step 1: Identify the leaving group in the starting material. In this case, the chlorine atom (Cl) is the leaving group. Under solvolysis conditions with CH3CH2OH and heat, the Cl will leave, forming a carbocation intermediate.
Step 2: Analyze the stability of the carbocation formed after the leaving group departs. The initial carbocation is a secondary carbocation (2°), which is less stable than a tertiary carbocation (3°). This instability drives the rearrangement.
Step 3: Propose a hydride shift or alkyl shift to stabilize the carbocation. In this case, a hydride shift occurs where a hydrogen atom (along with its bonding electrons) from the adjacent carbon migrates to the carbocation center. This results in the formation of a tertiary carbocation (3°), which is more stable due to increased hyperconjugation and inductive effects.
Step 4: Once the tertiary carbocation is formed, the nucleophile (CH3CH2OH) attacks the carbocation. The oxygen atom in ethanol donates a pair of electrons to form a bond with the carbocation, resulting in the formation of an ether product.
Step 5: Repeat the process for any alternative rearrangements that could lead to other products. In this case, the hydride shift leads to two possible tertiary carbocations, each of which reacts with ethanol to form the two observed ether products.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Carbocation Stability
Carbocations are positively charged carbon species that can rearrange to form more stable intermediates. Stability increases from primary to tertiary carbocations due to hyperconjugation and inductive effects. In solvolysis reactions, a hydride or alkyl shift can convert a less stable carbocation (like a secondary) into a more stable tertiary or resonance-stabilized carbocation, facilitating the reaction.
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05:58
Determining Carbocation Stability
Rearrangement Mechanisms
Rearrangement mechanisms, such as hydride shifts and alkyl shifts, involve the migration of hydrogen or alkyl groups to adjacent carbocations. These shifts occur to stabilize the carbocation by forming a more stable structure. Understanding these mechanisms is crucial for predicting the products of solvolysis reactions, as they dictate the pathway and stability of intermediates formed during the reaction.
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06:08Definition of Claisen Rearrangement
Solvolysis Reactions
Solvolysis reactions involve the substitution of a leaving group (like Cl) by a nucleophile (like an alcohol) in the presence of a solvent. The reaction typically proceeds through the formation of a carbocation intermediate, which can undergo rearrangement to enhance stability. The solvent can also stabilize the carbocation, influencing the reaction's rate and product distribution, making it essential to consider solvent effects in these reactions.
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Related Practice
Textbook Question
Benzyl bromide is a primary halide. It undergoes SN1 substitution about as fast as most tertiary halides. Use resonance structures to explain this enhanced reactivity.
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Textbook Question
For each reaction, give the expected substitution product, and predict whether the mechanism will be predominantly first order (SN1) or second order (SN2).
a. 2-chloro-2-methylbutane + CH3COOH
b. isobutylbromide + sodium methoxide
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Textbook Question
Give the SN1 mechanism for the formation of 2-ethoxy-3-methylbutane, the unrearranged product in this reaction.
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Textbook Question
Propose a mechanism involving a hydride shift or an alkyl shift for each solvolysis reaction. Explain how each rearrangement forms a more stable intermediate.
Hint: Most rearrangements convert 2° (or incipient 1°) carbocations to 3° or resonance-stabilized carbocations.
(c)
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Textbook Question
Propose a mechanism involving a hydride shift or an alkyl shift for each solvolysis reaction. Explain how each rearrangement forms a more stable intermediate.
Hint: Most rearrangements convert 2° (or incipient 1°) carbocations to 3° or resonance-stabilized carbocations.
(d)
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