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

13. Alcohols and Carbonyl Compounds

Grignard Reaction

Organic Chemistry

13. Alcohols and Carbonyl Compounds

Grignard Reaction

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Problem 9

Textbook Question

Addition to an epoxide occurs via an S_N2 reaction, but the stereochemistry of the epoxide is retained in the following reaction. Why?

Verified step by step guidance

Understand the mechanism of the reaction: The addition to an epoxide occurs via an Sₙ2 mechanism, which involves a backside attack by the nucleophile. This means the nucleophile attacks the less sterically hindered carbon of the epoxide ring, leading to ring opening.

Recognize the stereochemical implications of the Sₙ2 mechanism: In a typical Sₙ2 reaction, the stereochemistry at the carbon being attacked is inverted due to the backside attack. However, in the case of an epoxide, the stereochemistry of the product depends on the orientation of the epoxide ring during the attack.

Consider the retention of stereochemistry: The retention of stereochemistry in this reaction occurs because the nucleophile attacks the epoxide in such a way that the stereochemical configuration of the substituents on the epoxide is preserved. This happens because the epoxide ring is planar and the attack occurs in a concerted manner, maintaining the relative spatial arrangement of the groups.

Account for the reaction conditions: The reaction conditions, such as the solvent and the nature of the nucleophile, can influence the stereochemical outcome. For example, if the reaction occurs in a non-polar solvent, the nucleophile may approach the epoxide in a way that minimizes steric hindrance while preserving the stereochemistry.

Summarize the key point: The stereochemistry of the epoxide is retained because the nucleophile attacks in a manner that preserves the relative configuration of the substituents on the epoxide, even though the Sₙ2 mechanism typically involves inversion of configuration at the site of attack.

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Key Concepts

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

Epoxide Structure

Epoxides are three-membered cyclic ethers characterized by a highly strained ring structure. This strain makes them reactive, particularly towards nucleophiles. The oxygen atom in the epoxide contributes to the ring's reactivity, allowing for nucleophilic attack at the carbon atoms adjacent to the oxygen.

Sₙ2 Mechanism

The Sₙ2 (bimolecular nucleophilic substitution) mechanism involves a nucleophile attacking an electrophilic carbon atom from the opposite side of the leaving group, resulting in inversion of configuration. This concerted process means that the stereochemistry of the substrate is directly affected by the approach of the nucleophile, leading to a retention of stereochemistry in certain cases, such as with epoxides.

Stereochemistry Retention

In the context of epoxide reactions, stereochemistry retention occurs when the nucleophile attacks the less hindered carbon atom of the epoxide. Since the epoxide's ring structure forces the nucleophile to approach from the backside, the original stereochemical configuration is preserved, leading to a product that maintains the stereochemical characteristics of the starting epoxide.

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