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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4:27 minutes

Problem 47c

Textbook Question

Suggest an alkene that, in two steps, could be converted into each of the following ketones. Each sequence should involve a pinacol rearrangement.
(c)

Verified step by step guidance

Step 1: Identify the target ketone structure. The ketone shown has a carbonyl group on the terminal carbon of a chain, with a branched alkyl group attached to the second carbon. This suggests that the precursor molecule must have a hydroxyl group on the carbon adjacent to the carbonyl group after rearrangement.

Step 2: Recall the pinacol rearrangement mechanism. This reaction involves a vicinal diol (two hydroxyl groups on adjacent carbons) undergoing acid-catalyzed rearrangement to form a ketone. Therefore, the intermediate before the rearrangement must be a vicinal diol.

Step 3: Determine the alkene that can lead to the vicinal diol. Alkenes can be converted into vicinal diols via hydroxylation reactions, such as using osmium tetroxide (OsO₄) or potassium permanganate (KMnO₄). The alkene should have the correct substitution pattern to yield the desired diol.

Step 4: Propose the alkene structure. The alkene should have a double bond between the second and third carbons of the chain, with a methyl group attached to the second carbon. This substitution pattern ensures that hydroxylation will produce the correct vicinal diol.

Step 5: Outline the two-step process. First, perform hydroxylation of the alkene to produce the vicinal diol. Second, subject the vicinal diol to acid-catalyzed pinacol rearrangement to yield the target ketone.

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Key Concepts

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

Alkene Reactivity

Alkenes are hydrocarbons that contain a carbon-carbon double bond, making them reactive intermediates in organic reactions. Their reactivity is primarily due to the presence of the π bond, which can participate in various reactions such as electrophilic addition, oxidation, and rearrangement. Understanding the types of reactions that alkenes can undergo is crucial for designing synthetic pathways to target compounds.

Pinacol Rearrangement

The pinacol rearrangement is a chemical reaction that involves the conversion of a pinacol (a 1,2-diol) into a ketone or aldehyde through a rearrangement process. This reaction typically occurs under acidic conditions and involves the migration of an alkyl group and the formation of a carbocation intermediate. Recognizing how this rearrangement alters the structure of the starting material is essential for predicting the final product in synthetic routes.

Synthetic Strategy

A synthetic strategy in organic chemistry refers to the planned sequence of reactions and transformations used to construct a target molecule from simpler starting materials. This involves selecting appropriate reagents, reaction conditions, and intermediates to achieve the desired product efficiently. In the context of the question, devising a two-step synthesis involving an alkene and a pinacol rearrangement requires careful consideration of the starting materials and the desired ketone structure.

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Related Practice

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:

Textbook Question

Propose a mechanism for each reaction.

(a)

(b)

Textbook Question

The following reaction is called the pinacol rearrangement. The reaction begins with an acid-promoted ionization to give a carbocation. This carbocation undergoes a methyl shift to give a more stable, resonance-stabilized cation. Loss of a proton gives the observed product. Propose a mechanism for the pinacol rearrangement.

Textbook Question

Treatment of the following alcohol was expected to give alkene A. Instead, B was produced as the major product. Suggest a mechanism by which B formed.

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.

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Suggest an alkene that, in two steps, could be converted into each of the following ketones. Each sequence should involve a pinacol rearrangement.(c)

Key Concepts

Alkene Reactivity

Pinacol Rearrangement

Synthetic Strategy

Watch next

Suggest an alkene that, in two steps, could be converted into each of the following ketones. Each sequence should involve a pinacol rearrangement.
(c)