Textbook Question
When equivalent amounts of methyl bromide and sodium iodide are dissolved in methanol, the concentration of iodide ion quickly decreases and then slowly returns to its original concentration. Account for this observation.
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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 127a
Bruice 8th EditionCh. 9 - Substitution and Elimination Reactions of Alkyl HalidesProblem 127aChapter 10, Problem 127a
For each of the following compounds, draw the product that forms in an E2 reaction and indicate its configuration:
a. (1S,2S)-1-bromo-1,2-diphenylpropane
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Identify the substrate: The given compound is (1S,2S)-1-bromo-1,2-diphenylpropane. This is a secondary alkyl halide with a bromine atom attached to the first carbon and two phenyl groups attached to the first and second carbons.
Determine the mechanism: The problem specifies an E2 reaction. E2 (bimolecular elimination) reactions occur in a single concerted step, where a base abstracts a proton from a β-carbon (a carbon adjacent to the carbon bearing the leaving group), and the leaving group departs simultaneously, forming a double bond.
Analyze the stereochemistry: In an E2 reaction, the β-hydrogen and the leaving group (bromine in this case) must be antiperiplanar (in opposite planes and 180° apart) for the elimination to occur. Check the Newman projection or the 3D structure of the molecule to identify the antiperiplanar β-hydrogen.
Determine the product: Once the antiperiplanar β-hydrogen is identified, the base will abstract this proton, and the bromine will leave, forming a double bond between the α-carbon (carbon 1) and the β-carbon (carbon 2). The configuration of the product will depend on the stereochemistry of the starting material and the antiperiplanar geometry.
Indicate the configuration of the product: After forming the double bond, determine whether the product has an E (trans) or Z (cis) configuration based on the priority of the substituents attached to the double-bonded carbons, following the Cahn-Ingold-Prelog priority rules.
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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 β-carbon while a leaving group departs from the α-carbon, resulting in the formation of a double bond. This reaction is characterized by a single concerted step, meaning that bond breaking and bond formation occur simultaneously. The stereochemistry of the reactants significantly influences the product configuration, often leading to the formation of alkenes with specific stereochemical arrangements.
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Drawing the E2 Mechanism.
Stereochemistry and Configuration
Stereochemistry refers to the spatial arrangement of atoms in molecules and how this affects their chemical behavior. In the context of E2 reactions, the configuration of the starting material (R or S) can determine the stereochemical outcome of the product. The E2 mechanism typically favors the formation of the more stable alkene, which can be influenced by the relative positions of substituents on the double bond, leading to either cis or trans configurations.
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Substituent Effects on Elimination Reactions
The presence and position of substituents on the carbon chain can significantly affect the outcome of E2 reactions. Bulky groups can hinder the approach of the base to the β-hydrogen, while the orientation of substituents can dictate whether the reaction proceeds via a syn or anti elimination pathway. Understanding these effects is crucial for predicting the major product and its configuration in elimination reactions, especially in complex molecules like diphenylpropane.
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Related Practice
Textbook Question
What products are formed when the following stereoisomer of 2-chloro-1,3-dimethylcyclohexane reacts with methoxide ion?
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Textbook Question
Propose a mechanism for the following reaction.
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Textbook Question
Predict the product for the following reaction and write a mechanism to explain how it is formed.
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Textbook Question
For each of the following compounds, draw the product that forms in an E2 reaction and indicate its configuration:
b. (1S,2R)-1-bromo-1,2-diphenylpropane
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Textbook Question
Explain why the following alkyl halide does not undergo a substitution reaction, regardless of the base that is used.
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