Textbook Question
Which reaction in each of the following pairs takes place more rapidly? (EtOH is ethyl alcohol; Et2O is diethyl ether.)
d.
e.
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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 55c
Bruice 8th EditionCh. 9 - Substitution and Elimination Reactions of Alkyl HalidesProblem 55cChapter 10, Problem 55c
How will the rate of each of the following SN2 reactions change if it is carried out in a more polar solvent?
c. 
Verified step by step guidance1
Understand the SN2 reaction mechanism: SN2 reactions are bimolecular nucleophilic substitution reactions where the rate depends on both the concentration of the nucleophile and the substrate. The reaction occurs in a single step with a backside attack by the nucleophile, leading to the inversion of configuration at the carbon center.
Analyze the role of the solvent: Polar solvents can be classified as protic or aprotic. Protic solvents (e.g., water, alcohols) can form hydrogen bonds and stabilize the nucleophile, reducing its nucleophilicity. Aprotic solvents (e.g., acetone, DMSO) do not stabilize the nucleophile as much, allowing it to remain more reactive.
Consider the nucleophile (NH3): Ammonia (NH3) is a neutral nucleophile. In a more polar protic solvent, the nucleophile may be stabilized through hydrogen bonding, which can decrease its reactivity and slow down the SN2 reaction rate. In a polar aprotic solvent, the nucleophile remains more reactive, potentially increasing the reaction rate.
Evaluate the substrate (CH3CH2I): Ethyl iodide (CH3CH2I) is a good substrate for SN2 reactions due to the weak C-I bond and the relatively unhindered primary carbon. The substrate's reactivity is not significantly affected by the polarity of the solvent, but the solvent's effect on the nucleophile is crucial.
Conclude the impact of a more polar solvent: If the solvent is polar protic, the rate of the SN2 reaction may decrease due to stabilization of the nucleophile. If the solvent is polar aprotic, the rate may increase as the nucleophile remains more reactive. The specific change in rate depends on the type of polar solvent used.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
SN2 Reaction Mechanism
The SN2 (substitution nucleophilic bimolecular) reaction is a type of nucleophilic substitution where the nucleophile attacks the electrophile simultaneously as the leaving group departs. This concerted mechanism results in a single transition state and is characterized by a second-order rate law, meaning the reaction rate depends on the concentration of both the nucleophile and the substrate.
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Drawing the SN2 Mechanism
Polarity of Solvents
Polar solvents have a significant dipole moment, which allows them to stabilize charged species and transition states through solvation. In SN2 reactions, a more polar solvent can stabilize the nucleophile and the leaving group, potentially increasing the reaction rate by lowering the activation energy required for the reaction to proceed.
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Nucleophilicity and Solvent Effects
Nucleophilicity refers to the ability of a nucleophile to donate an electron pair to an electrophile. In polar solvents, nucleophilicity can be affected due to solvation effects; strong solvation can hinder the nucleophile's reactivity. Therefore, understanding how solvent polarity influences nucleophilicity is crucial for predicting the rate of SN2 reactions.
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Related Practice
Textbook Question
Would you expect acetate ion (CH3CO2−) to be a better nucleophile in an SN2 reaction with an alkyl halide carried out in methanol or in dimethyl sulfoxide?
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Textbook Question
How will the rate of each of the following SN2 reactions change if it is carried out in a more polar solvent?
b.
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Textbook Question
How will the rate of each of the following SN2 reactions change if it is carried out in a more polar solvent?
a.
1573
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Textbook Question
Amines are good nucleophiles, even though they are neutral. How would the rate of an SN2 reaction between an amine and an alkyl halide be affected if the polarity of the solvent is increased?
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1
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Textbook Question
Which reaction in each of the following pairs takes place more rapidly? (EtOH is ethyl alcohol; Et2O is diethyl ether.)
a.
b.
c.
1186
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1
rank