Ch. 9 - Alkenes II: Oxidation and Reduction

Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition

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Mullins 1st Edition

Ch. 9 - Alkenes II: Oxidation and Reduction

Problem 16a

Chapter 8, Problem 16a

Predict the product(s) when each of the following are reacted with mCPBA, making sure to indicate the relative stereochemical outcome. Indicate any racemic mixtures by drawing both enantiomers.
(a)

Verified step by step guidance

Understand the reagent: mCPBA (meta-chloroperoxybenzoic acid) is a peracid commonly used for epoxidation of alkenes. It adds an oxygen atom across the double bond to form an epoxide (a three-membered cyclic ether).

Analyze the substrate: Identify the alkene in the given molecule. The double bond is the reactive site where mCPBA will act to form the epoxide.

Determine the stereochemical outcome: The epoxidation reaction with mCPBA is stereospecific. If the alkene is cis (Z-configuration), the epoxide will retain the cis stereochemistry. If the alkene is trans (E-configuration), the epoxide will retain the trans stereochemistry.

Account for chirality: If the alkene is part of a chiral molecule or generates a chiral center upon epoxidation, consider the possibility of forming enantiomers. If the starting material is achiral, the product will be a racemic mixture of enantiomers.

Draw the product(s): Represent the epoxide product(s) with the correct stereochemistry. If a racemic mixture is formed, draw both enantiomers explicitly to indicate the outcome.

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Key Concepts

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

mCPBA and its Role in Organic Reactions

mCPBA, or meta-chloroperbenzoic acid, is a peracid commonly used in organic chemistry for the epoxidation of alkenes. It introduces an oxygen atom across the double bond, forming an epoxide, which is a three-membered cyclic ether. Understanding how mCPBA reacts with different substrates is crucial for predicting the products of these reactions.

Stereochemistry and Epoxide Formation

Stereochemistry refers to the spatial arrangement of atoms in molecules and how this affects their chemical behavior. When mCPBA reacts with alkenes, the stereochemical outcome of the epoxide can lead to different configurations (cis or trans) based on the starting alkene's geometry. Recognizing how stereochemistry influences the formation of products is essential for predicting the relative stereochemical outcomes.

Enantiomers and Racemic Mixtures

Enantiomers are pairs of molecules that are non-superimposable mirror images of each other, often resulting from chiral centers in a compound. When a reaction produces both enantiomers in equal amounts, it is termed a racemic mixture. Identifying and representing racemic mixtures is important in organic synthesis, especially when discussing the stereochemical outcomes of reactions involving chiral products.

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Related Practice

Textbook Question

Evidence for the concertedness of epoxide formation comes from the stereospecificity of the reaction. If step 2 of a hypothetical stepwise mechanism were slow enough to make the reaction non-concerted, how would the product distribution change?

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Textbook Question

How does the carbonyl in mCPBA weaken the O―O σ bond (i.e., make a better leaving group)?

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Textbook Question

Predict the product(s) when each of the following are reacted with mCPBA, making sure to indicate the relative stereochemical outcome. Indicate any racemic mixtures by drawing both enantiomers.

(d)

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Textbook Question

Suggest an alkene that could be used to make each of the following halohydrins.

(c)

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Textbook Question

Calculate the atom economy of the reaction in Figure 9.24. [Catalysts are not included in the atom economy calculation.]

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