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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 31d
Chapter 13, Problem 31d

What is the major product of the following reactions? Disregard stereoisomers:
d. Chemical reaction diagram showing allylic bromination with reactants and conditions, including NBS and peroxide.

Verified step by step guidance
1
Step 1: Recognize the reagent and reaction conditions. NBS (N-Bromosuccinimide) in the presence of heat (Δ) and peroxide is used for allylic bromination. This reaction selectively replaces a hydrogen atom at the allylic position with a bromine atom.
Step 2: Identify the allylic positions in the given molecule. The molecule is a substituted cyclohexene with two methyl groups. The allylic positions are the carbon atoms adjacent to the double bond.
Step 3: Determine the most reactive allylic position. The allylic position with the most stable radical intermediate will be favored. In this case, the allylic position adjacent to the methyl group is more stable due to hyperconjugation and inductive effects.
Step 4: Predict the major product. Bromine will replace the hydrogen atom at the most reactive allylic position, resulting in the formation of an allylic bromide.
Step 5: Disregard stereoisomers as instructed. The major product will be the allylic bromide formed at the most stable allylic position, without considering stereochemistry.

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Key Concepts

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

Allylic Bromination

Allylic bromination is a reaction where bromine is introduced at the allylic position of an alkene or alkane. This process typically involves the use of N-bromosuccinimide (NBS) in the presence of a radical initiator, such as peroxide, under heat. The reaction proceeds via a radical mechanism, where the allylic hydrogen is abstracted, forming a resonance-stabilized radical that can then react with bromine.
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Radical Mechanism

A radical mechanism involves the formation and reaction of free radicals, which are highly reactive species with unpaired electrons. In the context of allylic bromination, the reaction begins with the generation of radicals through the homolytic cleavage of the N–Br bond in NBS, followed by the abstraction of hydrogen from the allylic position. This mechanism is crucial for understanding how the product distribution is influenced by the stability of the resulting radicals.
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Regioselectivity

Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others when multiple possibilities exist. In allylic bromination, the stability of the radical intermediates determines the major product. More stable radicals, such as those formed at more substituted allylic positions, are favored, leading to a specific major product in the reaction. Understanding regioselectivity is essential for predicting the outcome of 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.

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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

The deuterium kinetic isotope effect for the halogenation of an alkane is defined in the following equation, where X･ = Cl･ or Br･

Predict whether chlorination or bromination would have a greater deuterium kinetic isotope effect.

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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:

c.

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