Textbook Question
How many stereoisomers are possible for the following alkenes?
(b)
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Ch. 8 - Alkenes I: Properties and Electrophilic Additions
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471
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Table of contents
- Ch. 2 - General Chemistry Translated: Finding the Electrons114
- Ch. 3 - Alkanes and Cycloalkanes: Properties and Conformational Analysis109
- Ch. 4 - Acids and Bases: Electron Flow144
- Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics118
- Ch. 6 - Stereoisomerism: Arrangement of Atoms in Space112
- Ch. 7 - Principles of Green (Organic) Chemistry3
- Ch. 8 - Alkenes I: Properties and Electrophilic Additions158
- Ch. 9 - Alkenes II: Oxidation and Reduction150
- Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions101
- Ch. 11 - Properties and Synthesis of Alkyl Halides: Radical Reactions108
- Ch. 12 - Substitution and Elimination: Reactions of Haloalkanes172
- Ch. 13 - Alcohols, Ethers and Related Compounds: Substitution and Elimination239
- Ch. 14 - Structural Identification I: Infrared Spectroscopy and Mass Spectrometry54
- Ch. 15 - Structural Identification II: Nuclear Magnetic Resonance Spectroscopy93
- Ch. 16 - Metals in Organic Chemistry48
- Ch. 17 - Carbonyl Addition Reactions: Aldehydes and Ketones45
- Ch. 18 - Nucleophilic Acyl Substitution I: Carboxylic Acids18
- Ch. 19 - Nucleophilic Acyl Substitution II: Carboxylic Acid Derivatives39
- Ch. 20 - Enolates: Carbonyl Addition and Substitution13
- Ch. 21 - Conjugated Systems I: Stability and Addition Reactions56
- Ch. 22 - Conjugated Systems II: Pericyclic Reactions54
- Ch. 23 - Benzene I: Aromatic Stability and Substitution Reactions64
- Ch. 24 - Benzene II: Reactions Influenced by the Aromatic Ring62
- Ch. 25 - Amines: Structure, Reactions, and Synthesis27
- Ch. 26 - Amino Acids, Proteins, and Peptide Synthesis9
- Ch. 27 - Carbohydrates, Nucleic Acids, and Lipids54
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
Chapter 7, Problem 67
Because of the angle strain present in cyclopropanes, they tend to open up in the presence of nearby radicals. Show a mechanism for the following reaction that demonstrates this principle.
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Begin by recognizing that the cyclopropane ring is highly strained due to its small bond angles. This strain makes it susceptible to ring-opening reactions, especially in the presence of radicals.
The presence of HBr and H2O2 suggests a radical mechanism. H2O2 can decompose to form hydroxyl radicals, which can initiate the radical chain reaction.
The hydroxyl radical abstracts a hydrogen atom from HBr, generating a bromine radical. This bromine radical is crucial for the next step of the mechanism.
The bromine radical attacks the cyclopropane ring, leading to the opening of the ring. This attack results in the formation of a new radical at the site where the ring opens.
The newly formed radical can then react with another molecule of HBr, abstracting a hydrogen atom and forming the final product with a bromine atom attached to the terminal carbon of the opened chain.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Angle Strain
Angle strain occurs when the bond angles in a molecule deviate from the ideal values, causing increased energy and instability. In cyclopropanes, the bond angles are approximately 60 degrees, which is significantly less than the ideal tetrahedral angle of 109.5 degrees. This strain makes cyclopropanes more reactive, particularly in the presence of radicals, as they seek to relieve this strain by breaking bonds.
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Radical Mechanism
A radical mechanism involves the formation and reaction of species with unpaired electrons, known as radicals. These highly reactive intermediates can initiate chain reactions, such as the opening of strained rings like cyclopropanes. Understanding how radicals interact with cyclopropanes is crucial for illustrating the mechanism of the reaction, as they can lead to the cleavage of C-C bonds and the formation of new products.
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Reaction Mechanism
A reaction mechanism is a step-by-step description of the process by which reactants transform into products. It outlines the sequence of bond-breaking and bond-forming events, including the involvement of intermediates like radicals. In the case of cyclopropanes, illustrating the mechanism helps to clarify how the angle strain facilitates the reaction and the specific steps taken during the bond cleavage and formation.
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Related Practice
Textbook Question
When using sulfuric acid, but in the absence of other nucleophiles like water or bromide ion, less stable alkenes can be isomerized to their more stable isomer. Provide a mechanism for these acid-catalyzed isomerization reactions. [This is one illustration of the principle of microscopic reversibility.]
(b)
1
views
Textbook Question
How many stereoisomers are possible for the following alkenes?
(c)
Textbook Question
When using sulfuric acid, but in the absence of other nucleophiles like water or bromide ion, less stable alkenes can be isomerized to their more stable isomer. Provide a mechanism for these acid-catalyzed isomerization reactions. [This is one illustration of the principle of microscopic reversibility.]
(c)
1
views
Textbook Question
How many stereoisomers are possible for the following alkenes?
(d)
1
views
Textbook Question
When using sulfuric acid, but in the absence of other nucleophiles like water or bromide ion, less stable alkenes can be isomerized to their more stable isomer. Provide a mechanism for these acid-catalyzed isomerization reactions. [This is one illustration of the principle of microscopic reversibility.]
(a)