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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1:20 minutes

Problem 26a

Textbook Question

Propose a mechanism for each reaction.
(a)

Verified step by step guidance

Step 1: Recognize the reaction type. This is an acid-catalyzed dehydration reaction where an alcohol is converted into an alkene using concentrated sulfuric acid (H₂SO₄) and heat.

Step 2: Protonation of the alcohol group. The hydroxyl group (-OH) on the cyclopentanol molecule is protonated by H₂SO₄, forming a good leaving group (water). The protonation step increases the electrophilicity of the carbon attached to the hydroxyl group.

Step 3: Formation of the carbocation intermediate. The protonated hydroxyl group leaves as water, generating a carbocation intermediate on the cyclopentane ring. This step is crucial for the subsequent rearrangement or elimination.

Step 4: Elimination of a proton to form the double bond. A base (often HSO₄⁻ or water) abstracts a proton from a β-carbon adjacent to the carbocation, leading to the formation of a double bond (alkene) in the cyclopentane ring.

Step 5: Verify the product. The final product is cyclopentene, an alkene formed by the elimination of water from cyclopentanol. The reaction follows Zaitsev's rule, favoring the most substituted alkene.

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Key Concepts

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

Reaction Mechanism

A reaction mechanism is a step-by-step description of how reactants transform into products in a chemical reaction. It outlines the sequence of elementary steps, including bond breaking and forming, and the intermediates involved. Understanding the mechanism helps predict the outcome of reactions and the conditions required for them to occur.

Types of Organic Reactions

Organic reactions can be classified into several types, including substitution, addition, elimination, and rearrangement reactions. Each type has distinct characteristics and mechanisms. Recognizing the type of reaction is crucial for proposing an accurate mechanism, as it influences the pathways and intermediates formed during the reaction.

Curved Arrow Notation

Curved arrow notation is a visual representation used in organic chemistry to illustrate the movement of electrons during a reaction. Arrows indicate the direction of electron flow, showing how bonds are broken and formed. Mastery of this notation is essential for accurately depicting reaction mechanisms and understanding the underlying electron transfer processes.

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Related Practice

Textbook Question

Propose mechanisms for the following reactions.

HINT: Alcohol dehydrations usually go through E1 elimination of the protonated alcohol, with a carbocation intermediate. Rearrangements are common.

Textbook Question

Under acid catalysis, tetrahydrofurfuryl alcohol reacts to give surprisingly good yields of dihydropyran. Propose a mechanism to explain this useful synthesis.

Textbook Question

When the following substituted cycloheptanol undergoes dehydration, one of the minor products has undergone a ring contraction. Propose a mechanism to show how this ring contraction occurs.

Textbook Question

Propose a mechanism for each reaction.

(c)

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)

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Propose a mechanism for each reaction.(a)

Key Concepts

Reaction Mechanism

Types of Organic Reactions

Curved Arrow Notation

Watch next

Propose a mechanism for each reaction.
(a)