Textbook Question
In the following allylic radicals, identify the carbon where the new C― Br bond is most likely to form in the second propagation step.
(c)
1
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Ch. 11 - Properties and Synthesis of Alkyl Halides: Radical Reactions
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
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Mullins 1st EditionCh. 11 - Properties and Synthesis of Alkyl Halides: Radical ReactionsProblem 32a
Mullins 1st EditionCh. 11 - Properties and Synthesis of Alkyl Halides: Radical ReactionsProblem 32aChapter 10, Problem 32a
Predict the products of the following allylic halogenation reactions.
(a) 
Verified step by step guidance1
Identify the allylic position in the given molecule. The allylic position is the carbon atom adjacent to a double bond.
Recognize that allylic halogenation typically involves the substitution of a hydrogen atom at the allylic position with a halogen atom, often using reagents like N-bromosuccinimide (NBS) in the presence of light or heat.
Consider the resonance stabilization of the allylic radical formed during the reaction. The allylic radical can delocalize its unpaired electron over the π system, leading to multiple resonance structures.
Determine the most stable resonance structure of the allylic radical, as this will guide the formation of the major product. The stability is often influenced by the degree of substitution at the allylic position.
Predict the final product by replacing the hydrogen atom at the allylic position with the halogen atom, taking into account the most stable resonance structure and the regioselectivity of the reaction.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Allylic Halogenation
Allylic halogenation is a reaction where a halogen atom is introduced at the allylic position of an alkene. This position is adjacent to a carbon-carbon double bond. The reaction typically involves the use of N-bromosuccinimide (NBS) in the presence of light or heat, which generates a radical that abstracts a hydrogen atom from the allylic position, allowing the halogen to attach there.
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The general mechanism of Allylic Halogenation.
Radical Mechanism
The radical mechanism is a chain reaction process involving initiation, propagation, and termination steps. In allylic halogenation, the initiation step generates radicals, often through the homolytic cleavage of a halogen molecule. Propagation involves the radical reacting with the substrate to form a new radical, which continues the chain reaction. Understanding this mechanism is crucial for predicting the products formed during the reaction.
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03:28The mechanism of Radical Polymerization.
Resonance Stabilization
Resonance stabilization is a concept where the stability of a molecule is increased due to the delocalization of electrons across multiple atoms. In allylic systems, the allylic radical formed during halogenation is stabilized by resonance, as the unpaired electron can be delocalized over the π system. This stabilization influences the regioselectivity of the reaction, often leading to multiple possible products depending on the structure of the starting material.
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03:43The radical stability trend.
Related Practice
Textbook Question
The fact that allylic halogenation results in formation of the most stable alkene suggests that it is under thermodynamic control. Thus, the second propagation step must be reversible. Suggest an arrow-pushing mechanism by which the less stable allylic halide might equilibrate to the more stable allylic halide.
Textbook Question
Predict the products of the following allylic halogenation reactions.
(c)
1
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Textbook Question
In the following allylic radicals, identify the carbon where the new C― Br bond is most likely to form in the second propagation step.
(b)
2
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Textbook Question
Predict the products of the following allylic halogenation reactions.
(d)
1
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Textbook Question
In the following allylic radicals, identify the carbon where the new C–Br bond is most likely to form in the second propagation step.
(a)
2
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