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

Dihydroxylation

Organic Chemistry

10. Addition Reactions

Dihydroxylation

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4:20 minutes

Problem 23

Textbook Question

The concertedness of the OsO₄ reaction results in both oxygens being added to the same face of the molecule (i.e., syn addition). How might these conditions be modified in order to prepare a trans-diol?

Verified step by step guidance

Understand the reaction: The OsO₄ reaction is a syn-dihydroxylation, meaning both hydroxyl groups are added to the same face of the alkene. This is due to the concerted mechanism of the reaction, where the osmium tetroxide adds to the π-bond in a single step.

Recognize the goal: To prepare a trans-diol, the hydroxyl groups must be added to opposite faces of the molecule (anti addition). This requires a different reaction mechanism or reagent.

Consider an alternative reaction: One common method to achieve anti-dihydroxylation is through the epoxidation of the alkene followed by acid-catalyzed ring opening. This involves two steps: (1) formation of an epoxide and (2) hydrolysis of the epoxide under acidic conditions.

Step 1: Use a peracid (e.g., mCPBA) to convert the alkene into an epoxide. The epoxide is a three-membered cyclic ether that forms via a concerted mechanism, maintaining the stereochemistry of the starting alkene.

Step 2: Perform an acid-catalyzed ring opening of the epoxide. Protonation of the epoxide makes it more electrophilic, and water or another nucleophile attacks the more substituted carbon (if regioselectivity is relevant), leading to anti addition of hydroxyl groups and forming the trans-diol.

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Key Concepts

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

Syn Addition

Syn addition refers to the process where two substituents are added to the same side of a double bond in a molecule. In the context of the OsO₄ reaction, this means that both oxygen atoms are added to the same face of the alkene, resulting in a syn-diol. Understanding this concept is crucial for grasping how stereochemistry is affected during reactions involving alkenes.

Trans-Diol Formation

Trans-diols are formed when two hydroxyl groups are added to opposite sides of a double bond. To achieve this from an OsO₄ reaction, one must modify the reaction conditions, such as using a different reagent or reaction pathway that allows for anti addition. This concept is essential for understanding how to manipulate reaction conditions to achieve desired stereochemical outcomes.

Reagents and Reaction Conditions

The choice of reagents and specific reaction conditions can significantly influence the outcome of organic reactions. In the case of forming a trans-diol, alternative reagents like peracids or using a two-step process with different conditions can facilitate anti addition. Recognizing how these factors interact is vital for predicting and controlling the stereochemistry of organic transformations.

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Related Practice

Textbook Question

Predict the product(s) that would result when the alkenes are allowed to react under the following conditions: (vi) 1. OsO₄ 2. NaHSO₃

(h)

Textbook Question

Predict the product(s) that would result when the alkenes are allowed to react under the following conditions: (vi) 1. OsO₄ 2. NaHSO₃

(k)

Textbook Question

At the beginning of Chapter 9, we stated that after finishing Chapters 8 and 9, we would have the ability to make a large variety of functional groups using related reactions. Show the reagent(s) necessary to convert 1-isobutylcyclohexene into the following molecules.

(b)

Textbook Question

(d)

Textbook Question

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

(b)

Textbook Question

When using a terminal alkene under the conditions shown here, explain why it is unnecessary to show the relative stereochemical outcome in the product.

Textbook Question

Which of molecules A–D would you expect to give a positive permanganate test? That is, which would result in a purple KMnO₄ solution turning brown?

(d)

Textbook Question

Predict the product(s) that would result when the alkenes are allowed to react under the following conditions: (v) mCPBA; (vi) 1. OsO₄ 2. NaHSO₃.

(e)

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The concertedness of the OsO4 reaction results in both oxygens being added to the same face of the molecule (i.e., syn addition). How might these conditions be modified in order to prepare a trans-diol?

Key Concepts

Syn Addition

Trans-Diol Formation

Reagents and Reaction Conditions

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The concertedness of the OsO₄ reaction results in both oxygens being added to the same face of the molecule (i.e., syn addition). How might these conditions be modified in order to prepare a trans-diol?