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Ch. 9 - Alkenes II: Oxidation and Reduction
Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
All textbooksMullins 1st EditionCh. 9 - Alkenes II: Oxidation and ReductionProblem 50a
Chapter 8, Problem 50a

One way to think about concerted reactions is to imagine them as being stepwise reactions where, besides the slowest step, all others have infinitesimally small activation energies. Considering the hypothetical stepwise mechanism and actual concerted mechanism of epoxide formation, show what a reaction coordinate diagram might look like for each possibility.
(a) Stepwise, hypothetical mechanism:
Reaction coordinate diagram illustrating stepwise and concerted mechanisms for epoxide formation with activation energy details.

Verified step by step guidance
1
Understand the concept of a reaction coordinate diagram: A reaction coordinate diagram plots the energy of a system as a function of the progress of the reaction. It helps visualize the energy changes during a chemical reaction, including intermediates and transition states.
For a stepwise mechanism, identify the key features: A stepwise mechanism involves multiple steps, each with its own transition state and intermediate. The diagram will show distinct energy peaks for each transition state and valleys for intermediates.
Sketch the stepwise mechanism: Begin by drawing the energy of the reactants on the left side of the diagram. Then, add a peak for the first transition state, followed by a valley for the intermediate. Repeat this process for subsequent steps, ensuring the final energy corresponds to the products.
Label the diagram: Clearly label the reactants, intermediates, transition states, and products. Indicate the activation energy (ΔE‡) for each step, which is the energy difference between the reactants/intermediates and their respective transition states.
Compare to a concerted mechanism: In a concerted mechanism, all bond-breaking and bond-forming events occur simultaneously in a single step. The reaction coordinate diagram for a concerted mechanism will have only one peak (transition state) and no intermediates, contrasting with the stepwise diagram.

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Key Concepts

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

Concerted Reactions

Concerted reactions occur in a single step where bonds are formed and broken simultaneously, leading to the formation of products without any intermediates. This mechanism is characterized by a transition state that represents the highest energy point along the reaction pathway, and it typically results in a more efficient process with fewer side reactions.
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Reaction Coordinate Diagram

A reaction coordinate diagram visually represents the energy changes during a chemical reaction. The x-axis typically shows the progress of the reaction, while the y-axis indicates the energy of the system. Key features include the reactants, products, transition states, and intermediates, allowing for a clear comparison between concerted and stepwise mechanisms.
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Stepwise Mechanism

A stepwise mechanism involves multiple discrete steps, each with its own transition state and activation energy. In this scenario, the slowest step, known as the rate-determining step, dictates the overall reaction rate. The presence of intermediates can lead to a more complex energy profile, often resulting in a higher overall activation energy compared to concerted mechanisms.
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Related Practice
Textbook Question

One way to think about concerted reactions is to imagine them as being stepwise reactions where, besides the slowest step, all others have infinitesimally small activation energies. Considering the hypothetical stepwise mechanism and actual concerted mechanism of epoxide formation, show what a reaction coordinate diagram might look like for each possibility.

(b) Concerted , actual mechanism (butterfly transition state:

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Textbook Question

Consider the Cope rearrangement, a reaction we describe in Chapter 20.

(a) Using the knowledge we have gained here in Chapter 9, suggest a one-step, concerted mechanism that explains the formation of B from A.

(b) Which side of the reaction would you expect to be favored? Justify your answer.

(c) Which product, A or B, would you expect to be hydrogenated with the more exothermic heat of hydrogenation?

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Textbook Question

In light of your answer to Assessment 9.47, predict the product of the following reactions we have seen previously where an alcohol is substituted for water.

(a)

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Textbook Question

In light of your answer to Assessment 9.47, predict the product of the following reactions we have seen previously where an alcohol is substituted for water.

(c)

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Textbook Question

Bromination of buta-1,3-diene with a single equivalent of Br2 can give either of two products. (a) Which of these products (A or B) would you predict to be more stable? Justify your answer.

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Textbook Question

In light of your answer to Assessment 9.47, predict the product of the following reactions we have seen previously where an alcohol is substituted for water.

(b)

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