Textbook Question
Classify each reaction as a substitution, an elimination, or neither. Identify the leaving group in each reaction, and the nucleophile in substitutions.
c.
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Ch.6 - Alkyl Halides; Nucleophilic Substitution
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 6, Problem 10d
Show how free-radical halogenation might be used to synthesize the following compounds. In each case, explain why we expect to get a single major product.
(d) 
Verified step by step guidance1
Step 1: Identify the target compound and analyze its structure. The compound shown is a brominated bicyclic structure with a bromine atom attached to the benzylic position of the bicyclic ring system. This position is particularly reactive due to the stability of the benzylic radical formed during the reaction.
Step 2: Understand the mechanism of free-radical halogenation. Free-radical halogenation involves three steps: initiation, propagation, and termination. In the initiation step, a halogen molecule (e.g., Br2) is split into two bromine radicals by heat or light. These radicals are highly reactive and initiate the reaction.
Step 3: Determine the most reactive site for halogenation. In this case, the benzylic position is the most reactive due to the resonance stabilization of the benzylic radical. When a hydrogen atom is abstracted from this position, the resulting radical is stabilized by delocalization of electrons into the aromatic ring.
Step 4: Predict the major product. Since the benzylic radical is highly stabilized, bromination will predominantly occur at this position, leading to the formation of the single major product shown in the image. Other positions on the bicyclic ring system are less reactive and unlikely to undergo halogenation.
Step 5: Explain why a single major product is expected. The regioselectivity of the reaction is driven by the stability of the intermediate radical. The benzylic radical is significantly more stable than radicals formed at other positions, ensuring that bromination occurs exclusively at this site under typical free-radical halogenation conditions.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Free-Radical Halogenation
Free-radical halogenation is a reaction where alkanes react with halogens (like bromine) in the presence of heat or light to form alkyl halides. This process involves the generation of free radicals, which are highly reactive species with unpaired electrons. The reaction proceeds through three main steps: initiation, propagation, and termination, leading to the substitution of hydrogen atoms with halogen atoms.
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Selectivity in Free-Radical Reactions
Selectivity in free-radical halogenation refers to the preference for the formation of certain products over others. This is influenced by the stability of the free radicals formed during the reaction. More stable radicals (like tertiary radicals) are favored, leading to a single major product when the substrate has a clear preference for one site of substitution, as seen in the provided compound.
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Mechanism of Bromination
The mechanism of bromination involves the formation of a bromine radical that abstracts a hydrogen atom from the substrate, creating a new radical. This radical can then react with another bromine molecule to form the brominated product. The specific structure of the compound in the image suggests that bromination will occur at a position that leads to a stable radical, thus resulting in a single major product due to the lack of competing sites for substitution.
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Related Practice
Textbook Question
Classify each reaction as a substitution, an elimination, or neither. Identify the leaving group in each reaction, and the nucleophile in substitutions.
b.
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Textbook Question
Show how free-radical halogenation might be used to synthesize the following compounds. In each case, explain why we expect to get a single major product.
(c)
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Textbook Question
Show how free-radical halogenation might be used to synthesize the following compounds. In each case, explain why we expect to get a single major product.
(a) 1-chloro-2,2-dimethylpropane (neopentyl chloride)
(b) 2-bromo-2-methylbutane
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Textbook Question
Classify each reaction as a substitution, an elimination, or neither. Identify the leaving group in each reaction, and the nucleophile in substitutions.
a.
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Textbook Question
The light-initiated reaction of 2,3-dimethylbut-2-ene with N-bromosuccinimide (NBS) gives two products:
b. The bromination of cyclohexene using NBS gives only one major product, as shown on the previous page. Explain why there is no second product from an allylic shift.
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