Textbook Question
When 1-chlorocyclohexene reacts with HBr, the major product is 1-bromo-1-chlorocyclohexane. Propose a mechanism for this reaction, and explain why your proposed intermediate is more stable than the other possible intermediate
Ch.8 - Reactions of Alkenes
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 8, Problem 4c
Show how you would accomplish the following synthetic conversions.
(c) 2−methylcyclohexanol → 1−bromo−1−methylcyclohexane
Verified step by step guidance1
Identify the functional group transformation: The starting material is 2-methylcyclohexanol (an alcohol), and the target compound is 1-bromo-1-methylcyclohexane (an alkyl halide). This indicates that the hydroxyl group (-OH) must be replaced with a bromine atom (Br).
Protonate the hydroxyl group to make it a better leaving group: Treat 2-methylcyclohexanol with a strong acid, such as HBr. The hydroxyl group will be protonated to form water (H₂O), which is a good leaving group.
Perform a carbocation rearrangement: When the water molecule leaves, a carbocation intermediate is formed. The initial carbocation will be at the 2-position, but a hydride shift will occur to form a more stable tertiary carbocation at the 1-position.
Introduce the bromine nucleophile: The bromide ion (Br⁻) from HBr will attack the carbocation at the 1-position, resulting in the formation of 1-bromo-1-methylcyclohexane.
Verify the stereochemistry: Since the reaction proceeds through a carbocation intermediate, the product will likely be a racemic mixture if the starting material is chiral. Ensure that the final product matches the desired structure.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Alcohol to Alkyl Halide Conversion
The conversion of alcohols to alkyl halides is typically achieved through a substitution reaction, where the hydroxyl group (-OH) of the alcohol is replaced by a halogen atom. This can be accomplished using reagents such as phosphorus tribromide (PBr3) or thionyl chloride (SOCl2), which facilitate the departure of the -OH group and introduce the halide.
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Rearrangement and Stability of Carbocations
In organic synthesis, the stability of carbocations plays a crucial role in determining the pathway of a reaction. When converting 2-methylcyclohexanol to 1-bromo-1-methylcyclohexane, the formation of a stable tertiary carbocation can be favored, which may involve rearrangement of the molecule to achieve a more stable intermediate before the final product is formed.
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Stereochemistry in Substitution Reactions
Stereochemistry is essential in substitution reactions, as the configuration of the starting material can influence the outcome of the reaction. In the case of 2-methylcyclohexanol, understanding the stereochemical arrangement of the reactant will help predict the stereochemical outcome of the product, particularly if the reaction proceeds via an SN1 or SN2 mechanism.
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Related Practice
Textbook Question
Predict the major products of the following reactions, and propose mechanisms to support your predictions.
(b)
HINT: Remember to write out complete structures, including all bonds and charges, when writing a mechanism or determining the course of a reaction.
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Textbook Question
Show how you would accomplish the following synthetic conversions.
(a) but−1−ene → 1−bromobutane
(b) but−1−ene → 2−bromobutane
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Textbook Question
Predict the products of the following hydration reactions.
a. 1−methylcyclopentene + dilute acid
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Textbook Question
Propose a mechanism to show how 3,3-dimethylbut-1-ene reacts with dilute aqueous H2SO4 to give 2,3-dimethylbutan-2-ol and a small amount of 2,3-dimethylbut-2-ene.
HINT: When predicting products for electrophilic additions, first draw the structure of the carbocation (or other intermediate) that results from electrophilic attack.
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Textbook Question
Show how you would accomplish the following synthetic conversions.
(d) 2−methylbutan-2-ol → 2-bromo-3-methylbutane
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