Textbook Question
Which species in each pair is more stable?
a.
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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 85b
Bruice 8th EditionCh. 9 - Substitution and Elimination Reactions of Alkyl HalidesProblem 85bChapter 10, Problem 85b
Indicate how each of the same factors affects an E2 reaction.
1. the strength of the base
2. the concentration of the base
3. the solvent
Verified step by step guidance1
The strength of the base: In an E2 reaction, the rate of the reaction depends on the strength of the base. A stronger base is more effective at abstracting a proton from the β-carbon, which facilitates the elimination process. For example, bases like hydroxide (OH⁻) or alkoxides (RO⁻) are commonly used in E2 reactions. The stronger the base, the faster the reaction proceeds.
The concentration of the base: The E2 reaction is bimolecular, meaning the rate depends on both the substrate and the base. Increasing the concentration of the base increases the likelihood of collisions between the base and the substrate, thereby increasing the reaction rate. This relationship can be expressed as rate = k[substrate][base].
The solvent: The choice of solvent can significantly affect the E2 reaction. Polar aprotic solvents, such as acetone or dimethyl sulfoxide (DMSO), are preferred because they do not solvate the base as strongly as polar protic solvents. This allows the base to remain more reactive, enhancing the rate of the E2 reaction. Polar protic solvents, like water or alcohols, can hinder the reaction by stabilizing the base through hydrogen bonding.
The mechanism of the E2 reaction: It is a concerted process where the base abstracts a proton from the β-carbon, the leaving group departs, and the π-bond forms simultaneously. The strength and concentration of the base, as well as the solvent, all influence the efficiency of this concerted mechanism.
Summary: To optimize an E2 reaction, use a strong base, ensure a high concentration of the base, and select a polar aprotic solvent to maximize the reaction rate and yield.
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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 type of elimination reaction where a base removes a proton from a substrate, leading to the simultaneous formation of a double bond and the expulsion of a leaving group. This concerted mechanism requires a strong base and typically occurs in a single step, making the reaction rate dependent on both the substrate and the base.
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Base Strength
The strength of the base is crucial in E2 reactions, as stronger bases are more effective at abstracting protons from the substrate. A strong base increases the rate of the E2 reaction by facilitating the removal of the hydrogen atom, which is essential for the formation of the double bond. Common strong bases include alkoxides and hydrides.
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Solvent Effects
The choice of solvent can significantly influence E2 reactions. Polar aprotic solvents, such as acetone or DMSO, are preferred as they stabilize the transition state without solvation of the base, enhancing its reactivity. In contrast, polar protic solvents can hinder the reaction by stabilizing the base, thus reducing its ability to deprotonate the substrate effectively.
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Related Practice
Textbook Question
Which species in each pair is more stable?
c.
d.
800
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Textbook Question
Draw the major product obtained when an alkyl halide in [PROBLEM 9-83] undergoes an E1 reaction.
c.
1293
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Textbook Question
Which species in each pair is more stable?
b.
1269
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Textbook Question
Draw the major product obtained when an alkyl halide in [PROBLEM 9-83] undergoes an E1 reaction.
d.
1074
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Textbook Question
Indicate how each of the following factors affects an E1 reaction:
1. the strength of the base
2. the concentration of the base
3. the solvent
1045
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