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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5:33 minutes

Problem 38a

Textbook Question

Propose mechanisms for the following reactions. Additional products may be formed, but your mechanism only needs to explain the products shown.
(a)
(Hint: Hydride shift)

Verified step by step guidance

Identify the type of reaction: This reaction involves the conversion of an alcohol (CH3-CH2-CH2-CH2-OH) to an alkene (CH2=CH-CH2CH3). This suggests an elimination reaction, likely an E1 mechanism due to the involvement of a hydride shift.

Step 1: Protonation of the alcohol group: The hydroxyl group (-OH) is a poor leaving group. In the presence of an acid, the -OH group is protonated to form water (H2O), which is a much better leaving group. This step forms a protonated alcohol intermediate.

Step 2: Loss of the leaving group: The protonated alcohol loses water (H2O), forming a carbocation intermediate. The initial carbocation formed is a primary carbocation (CH3-CH2-CH2-CH2+), which is unstable.

Step 3: Hydride shift: To stabilize the carbocation, a hydride shift occurs. A hydrogen atom (with its bonding electrons) from the adjacent carbon migrates to the carbocation center. This results in the formation of a more stable secondary carbocation (CH3-CH2-CH+-CH3).

Step 4: Formation of the alkene: A base (likely the conjugate base of the acid used in Step 1) abstracts a proton from a β-carbon (a carbon adjacent to the carbocation). This leads to the formation of a double bond, resulting in the final product, CH2=CH-CH2CH3.

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Key Concepts

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

Reaction Mechanisms

A reaction mechanism is a step-by-step description of how reactants transform into products during a chemical reaction. It outlines the sequence of elementary steps, including bond breaking and formation, and provides insight into the intermediates formed. Understanding mechanisms is crucial for predicting the outcome of reactions and for proposing accurate pathways for transformations.

Hydride Shift

A hydride shift is a type of rearrangement reaction where a hydride ion (H-) moves from one carbon atom to an adjacent carbon atom. This process often occurs in carbocation intermediates to stabilize them by forming a more stable carbocation. Recognizing when a hydride shift can occur is essential for predicting the products of reactions involving carbocations.

Alkene Formation

Alkene formation typically involves the elimination of a leaving group and the formation of a double bond between carbon atoms. In the context of the given reaction, understanding how alkenes are generated from alcohols through dehydration or rearrangement is vital. This knowledge helps in predicting the structure of the alkene product formed from the initial alcohol substrate.

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Textbook Question

Although 2-methyl-1,2-propanediol is an unsymmetrical vicinal diol, only one product is obtained when it is dehydrated in an acidic solution.

a. What is this product?

Textbook Question

A student was studying terpene synthesis, and she wanted to make the compound shown here. First she converted 3-bromo-6-methylcyclohexene to alcohol A. She heated alcohol A with sulfuric acid and purified one of the components (compound B) from the resulting mixture. Compound B has the correct molecular formula for the desired product.

Textbook Question

What is the product of the following reaction?

Textbook Question

Which of the following alcohols dehydrates the fastest when heated with acid?

Textbook Question

Predict the major products of acid-catalyzed dehydration of the following alcohols.

(c)

(d)

Textbook Question

A vicinal diol has OH groups on adjacent carbons. The dehydration of a vicinal diol is accompanied by a rearrangement called the pinacol rearrangement. Propose a mechanism for this reaction.

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.

(c)

Multiple Choice

Which of the following is an example of a dehydration reaction?

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