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Ch. 12 - Radicals
Bruice - Organic Chemistry 8th Edition
Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook
All textbooksBruice 8th EditionCh. 12 - RadicalsProblem 31c
Chapter 13, Problem 31c

What is the major product of the following reactions? Disregard stereoisomers:
c. Chemical reaction showing ethylbenzene reacting with NBS and peroxide, indicating side-chain halogenation.

Verified step by step guidance
1
Step 1: Recognize the reagent and reaction type. NBS (N-Bromosuccinimide) in the presence of heat (Δ) and peroxide is commonly used for allylic or benzylic bromination. This reaction selectively replaces a hydrogen atom at the allylic or benzylic position with a bromine atom.
Step 2: Identify the benzylic position in the given molecule. The structure contains a benzene ring with an isopropyl group attached. The benzylic position is the carbon directly attached to the benzene ring within the isopropyl group.
Step 3: Determine the stability of the radical intermediate. The benzylic radical formed during the reaction is highly stabilized due to resonance with the aromatic ring. This stabilization makes the benzylic position the preferred site for bromination.
Step 4: Predict the product. The bromine atom will replace one of the hydrogens at the benzylic position, resulting in the formation of a brominated product at this site.
Step 5: Disregard stereoisomers. Since the problem specifies to disregard stereoisomers, focus only on the major product formed at the benzylic position without considering stereochemical variations.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Side-Chain Halogenation

Side-chain halogenation is a reaction where a halogen atom replaces a hydrogen atom in the side chain of an organic molecule. This process typically involves the use of reagents like N-bromosuccinimide (NBS) in the presence of heat or light, which facilitates the formation of a radical intermediate. The reaction is selective for the most stable radical, leading to the formation of the major product.
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Radical Mechanism

The radical mechanism involves the formation and reaction of free radicals, which are highly reactive species with unpaired electrons. In the context of halogenation, the reaction proceeds through three main steps: initiation, propagation, and termination. The initiation step generates radicals, the propagation step involves the reaction of these radicals with the substrate, and the termination step leads to the recombination of radicals.
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NBS and Peroxide

N-bromosuccinimide (NBS) is a reagent commonly used for bromination reactions, particularly in the presence of peroxides. Peroxides facilitate the formation of bromine radicals from NBS under heat, promoting the radical halogenation process. This method is advantageous as it allows for selective bromination at the allylic or benzylic positions, which is crucial for determining the major product in the reaction.
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Related Practice
Textbook Question

When 2-methylpropane is monochlorinated in the presence of light at room temperature, 36% of the product is 2-chloro-2-methylpropane and 64% is 1-chloro-2-methylpropane. From these data, calculate how much easier it is to remove a hydrogen atom from a tertiary carbon than from a primary carbon under these conditions.

Textbook Question

Propose a mechanism to account for the products formed in the following reaction:

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Textbook Question

What is the major product of the following reactions? Disregard stereoisomers:

a.

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Textbook Question

What are the answers to Problem 29 when the same compounds are treated with Br2 at 125 °C?

c.

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Textbook Question

What is the major product of the following reactions? Disregard stereoisomers:

b.

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Textbook Question

What is the major product of the following reactions? Disregard stereoisomers:

d.

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