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 59
Bruice 8th EditionCh. 9 - Substitution and Elimination Reactions of Alkyl HalidesProblem 59Chapter 10, Problem 59
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−?
Verified step by step guidance1
Analyze the structure of (R)-1-chloro-1-phenylethane. It contains a chiral carbon bonded to a chlorine atom, a phenyl group, and an ethyl group. The reaction involves substitution of the chlorine atom with a hydroxyl group (-OH) to form (R)-1-phenyl-1-ethanol.
Consider the reaction mechanism. In water, the reaction is likely to proceed via an SN1 mechanism because water is a polar protic solvent that stabilizes the carbocation intermediate. The chlorine atom leaves, forming a carbocation, which is then attacked by water to form the alcohol.
In 1.0 M HO⁻ (a strong base), the reaction is more likely to proceed via an SN2 mechanism. The hydroxide ion directly attacks the carbon bonded to the chlorine atom, displacing the chlorine in a single step. However, SN2 reactions invert the stereochemistry at the chiral center, which would result in the (S)-enantiomer, not the (R)-enantiomer.
Compare the stereochemical outcomes of the two mechanisms. The SN1 mechanism in water can retain the (R)-configuration because the carbocation intermediate can be attacked from either side, but the starting material's configuration is more likely to be preserved. The SN2 mechanism in 1.0 M HO⁻ inverts the configuration, leading to the (S)-enantiomer.
Conclude that the reaction in water will form the most (R)-1-phenyl-1-ethanol because the SN1 mechanism is more favorable for retaining the (R)-configuration, while the reaction in 1.0 M HO⁻ will predominantly form the (S)-enantiomer due to the stereochemical inversion of the SN2 mechanism.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Nucleophilic Substitution Reactions
Nucleophilic substitution reactions involve the replacement of a leaving group by a nucleophile. In this context, the reaction of (R)-1-chloro-1-phenylethane with a nucleophile (water or HO−) is crucial for understanding how the stereochemistry of the product is influenced by the reaction conditions.
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Nucleophiles and Electrophiles can react in Substitution Reactions.
Stereochemistry and Inversion of Configuration
Stereochemistry refers to the spatial arrangement of atoms in molecules. In nucleophilic substitution, particularly with chiral centers, the configuration can change. The reaction conditions can favor either retention or inversion of configuration, which is essential for determining the stereochemical outcome of (R)-1-phenyl-1-ethanol.
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Solvent Effects on Reaction Mechanisms
The choice of solvent can significantly influence the mechanism of a reaction. Polar protic solvents like water can stabilize ions and facilitate certain pathways, while polar aprotic solvents can enhance nucleophilicity. Understanding how these solvents affect the reaction of (R)-1-chloro-1-phenylethane is key to predicting the formation of (R)-1-phenyl-1-ethanol.
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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
Identify the three products formed when 2-bromo-2-methylpropane is dissolved in a mixture of 80% ethanol and 20% water.
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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.
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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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