Textbook Question
Which reaction in each of the following pairs takes place more rapidly? (EtOH is ethyl alcohol; Et2O is diethyl ether.)
d.
e.
515
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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 58
Bruice 8th EditionCh. 9 - Substitution and Elimination Reactions of Alkyl HalidesProblem 58Chapter 10, Problem 58
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?
Verified step by step guidance1
Understand the role of the solvent in an SN2 reaction: In an SN2 reaction, the nucleophile attacks the electrophilic carbon of the alkyl halide in a single concerted step. The solvent can significantly influence the nucleophilicity of the nucleophile. Polar aprotic solvents enhance nucleophilicity, while polar protic solvents can hinder it by stabilizing the nucleophile through hydrogen bonding.
Analyze the solvents given: Methanol (CH3OH) is a polar protic solvent, meaning it has hydrogen atoms capable of forming hydrogen bonds with the nucleophile. Dimethyl sulfoxide (DMSO, (CH3)2SO) is a polar aprotic solvent, meaning it does not have hydrogen atoms that can form hydrogen bonds, but it can stabilize cations without significantly stabilizing the nucleophile.
Consider the acetate ion (CH3CO2−): The acetate ion is a negatively charged nucleophile. In a polar protic solvent like methanol, the acetate ion will be stabilized by hydrogen bonding, reducing its nucleophilicity. In contrast, in a polar aprotic solvent like DMSO, the acetate ion will not be stabilized by hydrogen bonding, allowing it to remain more reactive as a nucleophile.
Relate solvent effects to the SN2 reaction: Since SN2 reactions are favored by strong nucleophiles, the acetate ion will be a better nucleophile in DMSO (polar aprotic solvent) compared to methanol (polar protic solvent). This is because DMSO does not hinder the nucleophile's reactivity, whereas methanol does.
Conclude the comparison: Based on the solvent effects, the acetate ion (CH3CO2−) would be a better nucleophile in an SN2 reaction with an alkyl halide when the reaction is carried out in dimethyl sulfoxide (DMSO) rather than in methanol.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Nucleophilicity
Nucleophilicity refers to the ability of a species to donate an electron pair to an electrophile, forming a chemical bond. It is influenced by factors such as charge, electronegativity, and solvent effects. In general, negatively charged species like acetate ion are stronger nucleophiles than their neutral counterparts. Understanding nucleophilicity is crucial for predicting the outcome of nucleophilic substitution reactions.
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Nucleophilic Addition
Solvent Effects
The choice of solvent can significantly impact the rate and mechanism of nucleophilic substitution reactions. Polar protic solvents, like methanol, can stabilize ions through hydrogen bonding, potentially reducing nucleophilicity. In contrast, polar aprotic solvents, such as dimethyl sulfoxide (DMSO), do not stabilize anions as effectively, often leading to increased nucleophilicity. Recognizing how solvents influence reaction dynamics is essential for evaluating reaction conditions.
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S<sub>N</sub>2 Mechanism
The S<sub>N</sub>2 mechanism is a type of nucleophilic substitution reaction characterized by a single concerted step where the nucleophile attacks the electrophile, leading to the displacement of a leaving group. This mechanism is bimolecular, meaning the rate depends on the concentration of both the nucleophile and the substrate. Understanding the S<sub>N</sub>2 mechanism is vital for predicting reaction pathways and outcomes in organic chemistry.
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Related Practice
Textbook Question
Under which of the following reaction conditions will (R)-1-chloro-1-phenylethane form the most (R)-1-phenyl-1-ethanol: in water or in 1.0 M HO−?
590
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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?
c.
1425
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Textbook Question
What is the best way to prepare the following ethers using an alkyl halide and an alkoxide ion?
a.
b.
1507
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Textbook Question
What is the best way to prepare the following ethers using an alkyl halide and an alkoxide ion?
c.
d.
677
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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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