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Ch.6 - Alkyl Halides; Nucleophilic Substitution
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
All textbooksWade 9th EditionCh.6 - Alkyl Halides; Nucleophilic SubstitutionProblem 58c
Chapter 6, Problem 58c

Show the products you expect when each compound reacts with NBS with light shining on the reaction.
(c)

Verified step by step guidance
1
Step 1: Recognize that NBS (N-Bromosuccinimide) in the presence of light is used for allylic bromination. This reaction selectively replaces a hydrogen atom at the allylic position (the carbon adjacent to a double bond) with a bromine atom.
Step 2: Identify the allylic positions in the given compound. The compound contains a double bond, and the carbons adjacent to this double bond are the allylic positions. These are the carbons directly connected to the double bond but not part of it.
Step 3: Determine the most stable allylic radical that can form during the reaction. When the allylic hydrogen is abstracted, the resulting radical is stabilized by resonance. Draw resonance structures to confirm the stability of the allylic radical.
Step 4: Add a bromine atom to the allylic radical to form the brominated product. The bromine will attach to the carbon where the radical was formed.
Step 5: Consider regioselectivity and stereochemistry if applicable. If multiple allylic positions are available, the major product will typically form at the position that leads to the most stable radical intermediate. Draw the expected product(s) based on this analysis.

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Key Concepts

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

NBS (N-Bromosuccinimide) Reactivity

NBS is a reagent commonly used in organic chemistry for bromination reactions, particularly in the presence of light. It generates bromine radicals upon photolysis, which can abstract hydrogen atoms from alkenes or allylic positions, leading to the formation of brominated products. Understanding how NBS interacts with different functional groups is crucial for predicting the products of the reaction.
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Radical Mechanism

The reaction mechanism involving NBS and light typically follows a radical pathway. This includes initiation (formation of radicals), propagation (reaction of radicals with substrates), and termination (recombination of radicals). Recognizing the steps of radical mechanisms helps in predicting the outcome of reactions, especially in terms of regioselectivity and stereochemistry.
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Allylic Bromination

Allylic bromination refers to the substitution of hydrogen atoms at the allylic position (the carbon adjacent to a double bond) with bromine. This process is favored in reactions involving NBS and light, as the formation of a stable allylic radical intermediate allows for selective bromination. Understanding this concept is essential for determining the expected products when the compound in the question reacts with NBS.
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Related Practice
Textbook Question

A student adds NBS to a solution of 1-methylcyclohexene and irradiates the mixture with a sunlamp until all the NBS has reacted. After a careful distillation, the product mixture contains two major products of formula C7H11Br.

a. Draw the resonance forms of the three possible allylic free radical intermediates.

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Textbook Question

Propose mechanisms to account for the observed products in the following reactions.

(b)

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Textbook Question

Show the products you expect when each compound reacts with NBS with light shining on the reaction.

(a)

(b)

1
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Textbook Question

A student adds NBS to a solution of 1-methylcyclohexene and irradiates the mixture with a sunlamp until all the NBS has reacted. After a careful distillation, the product mixture contains two major products of formula C7H11Br.

b. Rank these three intermediates from most stable to least stable.

2
views
Textbook Question

Propose mechanisms to account for the observed products in the following reactions.

(a)

2
views
Textbook Question

A student adds NBS to a solution of 1-methylcyclohexene and irradiates the mixture with a sunlamp until all the NBS has reacted. After a careful distillation, the product mixture contains two major products of formula C7H11Br.

(a) Draw the resonance forms of the three possible allylic free radical intermediates.

(b) Rank these three intermediates from most stable to least stable.

(c) Draw the products obtained from each free-radical intermediate.

3
views