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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2:49 minutes

Problem 39

Textbook Question

The following reaction resembles the acid-catalyzed cyclization of squalene oxide. Propose a mechanism for this reaction.

Verified step by step guidance

Step 1: Protonation of the epoxide group occurs first. The acidic environment (H⁺) protonates the oxygen atom in the epoxide, making it more electrophilic and susceptible to nucleophilic attack. This step generates a positively charged intermediate.

Step 2: The protonated epoxide undergoes ring opening. The strain in the three-membered ring is relieved as one of the bonds between the oxygen and carbon breaks, forming a carbocation intermediate. The position of the carbocation depends on the stability of the resulting structure.

Step 3: A hydride shift or methyl shift may occur to stabilize the carbocation. This rearrangement leads to the formation of a more stable tertiary carbocation, which is crucial for the subsequent cyclization step.

Step 4: Intramolecular nucleophilic attack occurs. The hydroxyl group (from water) attacks the carbocation, leading to the formation of a new bond and initiating the cyclization process. This step forms a cyclic intermediate.

Step 5: Deprotonation occurs to neutralize the intermediate. A water molecule or another base removes the excess proton, resulting in the final product with two hydroxyl groups and a methyl group attached to the cyclized structure.

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Key Concepts

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

Acid-Catalyzed Reactions

Acid-catalyzed reactions involve the use of an acid to increase the rate of a chemical reaction. In organic chemistry, acids can protonate reactants, making them more electrophilic and facilitating nucleophilic attacks. This is crucial in mechanisms like the cyclization of squalene oxide, where the acid activates the carbonyl group, promoting the formation of cyclic structures.

Cyclization Mechanisms

Cyclization mechanisms refer to the processes by which linear or branched molecules form cyclic structures. In the case of squalene oxide, the reaction involves the formation of a ring through the nucleophilic attack of a hydroxyl group on a carbocation intermediate. Understanding the steps of cyclization is essential for predicting the products and intermediates in such reactions.

Squalene and Its Derivatives

Squalene is a natural organic compound and a precursor to many steroids and terpenes. Its derivatives, like squalene oxide, undergo various transformations, including cyclization, under acidic conditions. Familiarity with the structure and reactivity of squalene and its derivatives is important for understanding the specific reaction mechanism and the resulting products in the context of organic synthesis.

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Related Practice

Textbook Question

Propylene oxide is a chiral molecule. Hydrolysis of propylene oxide gives propylene glycol, another chiral molecule.

(a) Draw the enantiomers of propylene oxide.

(b) Propose a mechanism for the acid-catalyzed hydrolysis of pure (R)-propylene oxide.

Textbook Question

Predict the major products of the following reactions, including stereochemistry.

f. trans-pent-2-ene + peroxyacetic acid in water

Textbook Question

a. Propose a mechanism for the conversion of cis-hex-3-ene to the epoxide (3,4-epoxyhexane) and the ring-opening reaction to give the glycol, hexane-3,4-diol. In your mechanism, pay particular attention to the stereochemistry of the intermediates and products.

b. Repeat part (a) for trans-hex-3-ene. Compare the products obtained from cis- and trans-hex-3-ene. Is this reaction sequence stereospecific?

Textbook Question

Predict the major product when each reagent reacts with ethylene oxide.

(d) PhNH₂ (aniline)

(e) KCN (potassium cyanide)

(f) NaN₃ (sodium azide)

Textbook Question

Predict the major products of the following reactions, including stereochemistry where appropriate.

(d) (2S,3R)-2-ethyl-2,3-dimethyloxirane + H⁺ / CH₃OH

Textbook Question

Under the right conditions, the following acid-catalyzed double cyclization proceeds in remarkably good yields. Propose a mechanism. Does this reaction resemble a biological process you have seen?

Textbook Question

Predict the product(s) that would result when the alkenes are allowed to react under the following conditions: (vii) 1. mCPBA 2. H₂SO₄, H₂O

(d)

Textbook Question

Predict the product(s) that would result when the alkenes are allowed to react under the following conditions: (vii) 1. mCPBA 2. H₂SO₄, H₂O

(k)

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