Textbook Question
What is the major product formed when the following compounds undergo an E1 reaction?
c.
2
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Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
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Bruice 8th EditionCh. 9 - Substitution and Elimination Reactions of Alkyl HalidesProblem 36
Bruice 8th EditionCh. 9 - Substitution and Elimination Reactions of Alkyl HalidesProblem 36Chapter 10, Problem 36
Why do cis-1-bromo-2-ethylcyclohexane and trans-1-bromo-2-ethylcyclohexane form different major products when they undergo an E2 reaction?
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Understand the E2 reaction mechanism: The E2 (bimolecular elimination) reaction involves the simultaneous removal of a β-hydrogen and a leaving group (in this case, bromine) to form a double bond. The reaction requires an anti-periplanar geometry, where the β-hydrogen and the leaving group are in opposite planes (one axial up and the other axial down in a cyclohexane ring).
Analyze the conformations of cis-1-bromo-2-ethylcyclohexane: In the cis isomer, the bromine atom and the ethyl group are on the same side of the cyclohexane ring. When the molecule adopts a chair conformation, the bromine will be in an axial position, and the ethyl group will be in an equatorial position. This allows for an anti-periplanar β-hydrogen to be available for elimination.
Analyze the conformations of trans-1-bromo-2-ethylcyclohexane: In the trans isomer, the bromine atom and the ethyl group are on opposite sides of the cyclohexane ring. In the chair conformation, the bromine will be in an equatorial position, and the ethyl group will be in an axial position. This changes the availability of anti-periplanar β-hydrogens for elimination.
Determine the major product for each isomer: In the cis isomer, the anti-periplanar geometry allows for elimination to occur more readily, leading to the formation of a specific alkene. In the trans isomer, the equatorial position of the bromine limits the availability of anti-periplanar β-hydrogens, which can lead to a different major product or a less favorable elimination pathway.
Conclude why the products differ: The difference in the spatial arrangement of substituents (cis vs. trans) affects the anti-periplanar geometry required for the E2 reaction. This results in different β-hydrogens being eliminated and, consequently, different alkenes being formed as the major products for the cis and trans isomers.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
E2 Reaction Mechanism
The E2 (bimolecular elimination) reaction is a concerted mechanism where a base abstracts a proton while a leaving group departs, resulting in the formation of a double bond. The stereochemistry of the reactants significantly influences the outcome, as the reaction requires an anti-periplanar arrangement of the leaving group and the hydrogen being removed.
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Stereochemistry of Substituents
Cis and trans isomers differ in the spatial arrangement of their substituents around a ring or double bond. In the case of 1-bromo-2-ethylcyclohexane, the relative positions of the bromine and ethyl groups affect the accessibility of the hydrogen atoms for elimination, leading to different major products in the E2 reaction based on whether the substituents are on the same side (cis) or opposite sides (trans).
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Regioselectivity and Stereoselectivity
Regioselectivity refers to the preference for the formation of one structural isomer over others in a chemical reaction, while stereoselectivity indicates the preference for one stereoisomer over another. In the E2 reaction of cis- and trans-1-bromo-2-ethylcyclohexane, the spatial arrangement of substituents leads to different major products due to these selectivity principles, influencing which double bond is formed.
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Related Practice
Textbook Question
Draw the substitution and elimination products for the following reactions, showing the configuration of each product:
b. cis-1-chloro-2-methylcyclohexane + CH3O−
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Textbook Question
What is the major product formed when the following compounds undergo an E1 reaction?
b.
2
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Textbook Question
What is the major product formed when the following compounds undergo an E1 reaction?
a.
3
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Textbook Question
Which isomer reacts more rapidly in an E2 reaction: cis-1-bromo-4-tert-butylcyclohexane or trans-1-bromo-4-tert-butylcyclohexane? Explain your answer.
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Textbook Question
Draw the substitution and elimination products for the following reactions, showing the configuration of each product:
a. trans-1-chloro-2-methylcyclohexane + CH3O−
1
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