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

9. Alkenes and Alkynes

Dehydration Reaction

Organic Chemistry

9. Alkenes and Alkynes

Dehydration Reaction

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8:08 minutes

Problem 73

Textbook Question

Write a mechanism that explains the formation of the following product. In your mechanism, explain the cause of the rearrangement, and explain the failure to form the Zaitsev product.

Verified step by step guidance

Step 1: Protonation of the alcohol group - The reaction begins with the protonation of the hydroxyl group (-OH) on the CH2OH substituent by sulfuric acid (H2SO4). This forms a good leaving group, water (H2O), and converts the alcohol into a positively charged intermediate.

Step 2: Formation of a carbocation - The water molecule leaves, resulting in the formation of a carbocation at the CH2 position. This carbocation is initially a primary carbocation, which is unstable.

Step 3: Carbocation rearrangement - To stabilize the carbocation, a hydride shift occurs. A hydrogen atom from the adjacent bridgehead carbon migrates to the carbocation center, resulting in a more stable tertiary carbocation. This rearrangement is driven by the increased stability of tertiary carbocations compared to primary carbocations.

Step 4: Elimination reaction - Under the influence of heat, a β-hydrogen is removed from the tertiary carbocation, leading to the formation of a double bond. The elimination follows the E1 mechanism, where the leaving group departs first, followed by the elimination of the β-hydrogen.

Step 5: Explanation of product formation - The product formed is not the Zaitsev product because the steric constraints of the bicyclic structure favor the formation of the less substituted alkene. The bulky nature of the bicyclic system prevents the formation of the more substituted double bond, which would typically be favored in Zaitsev's rule.

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Key Concepts

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

Elimination Reactions

Elimination reactions involve the removal of atoms or groups from a molecule, resulting in the formation of a double bond. In organic chemistry, these reactions can follow either an E1 or E2 mechanism, depending on the conditions and the structure of the substrate. Understanding the type of elimination is crucial for predicting the products formed, including the possibility of rearrangements.

Zaitsev's Rule

Zaitsev's Rule states that in elimination reactions, the more substituted alkene (the more stable product) is typically favored. This is due to the stability of the alkene formed, as more substituted alkenes have lower energy and are more thermodynamically stable. However, certain conditions, such as steric hindrance or the presence of strong bases, can lead to the formation of less substituted products instead.

Carbocation Rearrangement

Carbocation rearrangement occurs when a carbocation intermediate shifts to a more stable configuration during a reaction. This can involve hydride shifts or alkyl shifts, leading to the formation of a more stable carbocation. Understanding this concept is essential for predicting the outcome of reactions, especially when explaining why a particular product is formed instead of the expected Zaitsev product.

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Related Practice

Textbook Question

Propose mechanisms for the following reactions. In most cases, more products are formed than are shown here. You only need to explain the formation of the products shown, however.

(b)

Textbook Question

Write a balanced equation for each reaction, showing the major product you expect.

(a)

Textbook Question

Write a balanced equation for each reaction, showing the major product you expect.

(c)

Textbook Question

Show the product(s) you expect from dehydration of the following alcohols when they are heated in sulfuric or phosphoric acid. In each case, use a mechanism to show how the products are formed.

(c)

Textbook Question

Predict the products of the sulfuric acid-catalyzed dehydration of the following alcohols. When more than one product is expected, label the major and minor products.

(d) 1-isopropylcyclohexanol

(e) 2-methylcyclohexanol

Textbook Question

Propose mechanisms for the following reactions. Additional products may be formed, but your mechanism only needs to explain the products shown.

(b)

Textbook Question

Four pairs of compounds are shown. In each pair, one of the compounds reacts more quickly, or with a more favorable equilibrium constant, than the less conjugated system. In each case, explain the enhanced reactivity.

(c)

Textbook Question

Predict the product of the following pinacol rearrangements.

(b)

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