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

Epoxide Reactions

Organic Chemistry

10. Addition Reactions

Epoxide Reactions

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6:24 minutes

Problem 27c,d

Textbook Question

Predict the major products of the following reactions, including stereochemistry where appropriate.
(c) (2S,3R)-2-ethyl-2,3-dimethyloxirane + CH₃O^– / CH₃OH
(d) (2S,3R)-2-ethyl-2,3-dimethyloxirane + H⁺ / CH₃OH

Verified step by step guidance

Step 1: Recognize the type of reaction. Both reactions involve the opening of the epoxide ring in (2S,3R)-2-ethyl-2,3-dimethyloxirane. In part (c), the reaction occurs under basic conditions (CH3O- / CH3OH), while in part (d), the reaction occurs under acidic conditions (H+ / CH3OH). The mechanism and regioselectivity differ depending on the conditions.

Step 2: Analyze the mechanism for part (c) (basic conditions). Under basic conditions, the nucleophile (CH3O-) attacks the less sterically hindered carbon of the epoxide ring. This occurs via an SN2 mechanism, leading to inversion of stereochemistry at the attacked carbon. The product will have the methoxy group (-OCH3) added to the less substituted carbon, and the stereochemistry at this carbon will be inverted.

Step 3: Analyze the mechanism for part (d) (acidic conditions). Under acidic conditions, the epoxide ring is protonated by H+, making it more electrophilic. The nucleophile (CH3OH) then attacks the more substituted carbon of the epoxide ring due to the stability of the carbocation-like transition state. This occurs via an SN1-like mechanism, leading to retention of stereochemistry at the attacked carbon. The product will have the methoxy group (-OCH3) added to the more substituted carbon.

Step 4: Consider stereochemistry. For part (c), the stereochemistry at the less substituted carbon is inverted due to the SN2 mechanism. For part (d), the stereochemistry at the more substituted carbon is retained due to the SN1-like mechanism. Ensure that the stereochemistry of the products is clearly indicated in the final structures.

Step 5: Draw the major products for both reactions. For part (c), the product will have the methoxy group added to the less substituted carbon with inversion of stereochemistry. For part (d), the product will have the methoxy group added to the more substituted carbon with retention of stereochemistry. Verify that the stereochemistry matches the expected outcome based on the mechanisms described.

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Key Concepts

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

Epoxide Reactivity

Epoxides are three-membered cyclic ethers that are highly reactive due to the strain in their ring structure. They can undergo nucleophilic ring-opening reactions, where a nucleophile attacks the less hindered carbon atom, leading to the formation of alcohols or other functional groups. Understanding the mechanism of epoxide ring-opening is crucial for predicting the products of reactions involving epoxides.

Stereochemistry

Stereochemistry refers to the spatial arrangement of atoms in molecules and how this affects their chemical behavior. In reactions involving chiral centers, such as the one in the given question, the stereochemistry of the reactants can influence the stereochemical outcome of the products. Recognizing the stereochemical configuration of reactants is essential for predicting the stereochemical outcomes of the reactions.

Acid-Catalyzed Reactions

Acid-catalyzed reactions involve the use of an acid to facilitate the reaction process, often by protonating a functional group to make it more reactive. In the context of the given question, the presence of H+ in the reaction with methanol suggests that the epoxide will be protonated, leading to a more favorable pathway for nucleophilic attack. Understanding how acids influence reaction mechanisms is key to predicting the products formed.

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Predict the major products of the following reactions, including stereochemistry where appropriate.(c) (2S,3R)-2-ethyl-2,3-dimethyloxirane + CH3O– / CH3OH(d) (2S,3R)-2-ethyl-2,3-dimethyloxirane + H+ / CH3OH

Key Concepts

Epoxide Reactivity

Stereochemistry

Acid-Catalyzed Reactions

Watch next

Predict the major products of the following reactions, including stereochemistry where appropriate.
(c) (2S,3R)-2-ethyl-2,3-dimethyloxirane + CH₃O^– / CH₃OH
(d) (2S,3R)-2-ethyl-2,3-dimethyloxirane + H⁺ / CH₃OH