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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7:02 minutes

Problem 61b

Textbook Question

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

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 cyclopentylmethanol molecule 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 benzylic position (the carbon attached to the cyclopentane ring). This carbocation is stabilized due to its proximity to the ring structure.

Step 3: Elimination to form alkenes - The carbocation undergoes elimination reactions to form the observed alkene products. A β-hydrogen is removed from adjacent carbons, leading to the formation of double bonds. This results in the formation of cyclopentene and methylenecyclopentane as products.

Step 4: Rearrangement to form cyclohexene - The carbocation can undergo a ring expansion via a hydride or alkyl shift, leading to the formation of a six-membered ring. This rearrangement results in the formation of cyclohexene as an additional product.

Step 5: Final products - The reaction yields three products: cyclopentene, methylenecyclopentane, and cyclohexene. These products are formed through elimination and rearrangement mechanisms facilitated by the acidic conditions and heat.

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Key Concepts

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

Acid-Base Reactions

Acid-base reactions are fundamental in organic chemistry, where an acid donates a proton (H+) and a base accepts it. In the context of the given reaction involving H2SO4, a strong acid, understanding how protons are transferred is crucial for predicting the formation of products. This concept helps in identifying the reactive sites in molecules and the resulting changes in their structure.

Reaction Mechanisms

A reaction mechanism outlines the step-by-step sequence of elementary reactions that lead to the formation of products. It is essential to propose a mechanism for the reactions shown, as it provides insight into the intermediates formed and the transition states involved. Understanding mechanisms allows chemists to predict the outcome of reactions and the stability of intermediates.

Thermal Decomposition

Thermal decomposition refers to the process where a compound breaks down into simpler substances when heated. In the context of the reaction with heat, recognizing how heat influences the stability of reactants and products is vital. This concept is particularly relevant for understanding how certain functional groups may rearrange or eliminate under heat, leading to the formation of multiple products.

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Related Practice

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

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.

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

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)

Textbook Question

Propose a mechanism for each of the following reactions:

Textbook Question

Propose a mechanism for each of the following reactions:

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