Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

10. Addition Reactions

Epoxidation

Organic Chemistry

10. Addition Reactions

Epoxidation

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Problem 14

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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The O―O σ bond in peroxides, such as hydrogen peroxide (HO―OH), is inherently weak due to the repulsion between the lone pairs on the adjacent oxygen atoms. This bond can be further weakened by electronic effects from substituents.

In mCPBA (meta-chloroperoxybenzoic acid), the carbonyl group (C=O) is highly electronegative and withdraws electron density from the adjacent oxygen atoms through resonance and inductive effects.

The electron-withdrawing nature of the carbonyl group stabilizes the negative charge on the leaving group (the oxygen atom) when the O―O bond breaks, making the bond easier to cleave.

Additionally, the resonance structure of mCPBA allows delocalization of electrons from the carbonyl group, further reducing electron density on the O―O bond and weakening it.

The presence of the aromatic ring and the chlorine substituent in mCPBA also contributes to the electron-withdrawing effects, enhancing the ability of the O―O bond to act as a better leaving group compared to hydrogen peroxide.

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Key Concepts

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

Carbonyl Group Reactivity

The carbonyl group (C=O) is highly polar, with a partial positive charge on the carbon atom and a partial negative charge on the oxygen. This polarity makes the carbonyl carbon susceptible to nucleophilic attack, which can lead to the formation of more reactive intermediates. In the context of mCPBA, the carbonyl's reactivity plays a crucial role in facilitating the weakening of the O―O bond.

Peroxide Bond Strength

The O―O bond in peroxides, such as mCPBA, is relatively weak compared to other covalent bonds. This weakness is due to the repulsion between the lone pairs of electrons on the oxygen atoms. When the carbonyl group interacts with the peroxide, it can stabilize the transition state, leading to a decrease in the O―O bond strength and making it a better leaving group during reactions.

Leaving Group Ability

A leaving group is an atom or group that can depart from the parent molecule during a chemical reaction, often taking with it a pair of electrons. The ability of a leaving group to depart is influenced by its stability after leaving. In the case of mCPBA, the weakening of the O―O bond enhances the leaving group's ability, as the resulting species can be more stable, thus facilitating the overall reaction.

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Related Practice

Textbook Question

When producing a chiral molecule, epoxide formation still results in a mixture of enantiomers, despite its stereospecificity.

(b) How is it that a reaction can be stereospecific while still producing two enantiomers?

Textbook Question

Rank the reactivity of the following alkenes with mCPBA ( 1 = most reactive , 5 least reactive ).

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.

(a) Stepwise, hypothetical mechanism:

Textbook Question

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

Textbook Question

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

Textbook Question

Write the appropriate reagent over each arrow.

Textbook Question

In addition to using mCPBA, epoxides can be synthesized from alkenes in the two-step process shown. Give a mechanism for each step of the process.

Textbook Question

In Chapter 9, electron-rich alkenes were oxidized under acidic conditions with mCPBA. Conjugated alkenes can be oxidized using the same reagent, but under basic conditions. Suggest a mechanism for this reaction. [Think about what is electron-rich and what is electron-poor in the reaction. Also, identify the bonds formed and broken.]

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