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

10. Addition Reactions

Alkyne Oxidative Cleavage

Organic Chemistry

10. Addition Reactions

Alkyne Oxidative Cleavage

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5:10 minutes

Problem 24b

Textbook Question

Oxidative cleavages can help to determine the positions of the triple bonds in alkynes.
(b) An unknown alkyne undergoes oxidative cleavage to give the following triacid plus one equivalent of propionic acid. Propose a structure for the alkyne.

Verified step by step guidance

Step 1: Understand the reaction conditions. The unknown alkyne undergoes oxidative cleavage using ozone (O₃) at -78°C followed by hydrolysis with water (H₂O). This reaction breaks the triple bond in the alkyne, forming carboxylic acids as products.

Step 2: Analyze the products. The reaction yields two products: (1) a triacid with the structure HOOC-(CH₂)₇-CH(COOH)-COOH and (2) one equivalent of propionic acid (CH₃CH₂COOH). This indicates that the alkyne has two triple bonds, as oxidative cleavage of each triple bond produces carboxylic acids.

Step 3: Deduce the positions of the triple bonds. The triacid product suggests that one triple bond is located such that cleavage results in a molecule with three carboxylic acid groups. The propionic acid indicates that the second triple bond is located such that cleavage produces a three-carbon carboxylic acid.

Step 4: Reconstruct the alkyne structure. To form the triacid, the alkyne must have a segment with a chain of 7 methylene groups (CH₂) between the triple bonds. The propionic acid suggests that the second triple bond is at the end of the chain, adjacent to a methyl group.

Step 5: Combine the information. The unknown alkyne structure can be proposed by placing the two triple bonds in positions that align with the cleavage products: one triple bond near the center of the chain to form the triacid and the other at the end to form propionic acid.

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Key Concepts

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

Oxidative Cleavage

Oxidative cleavage is a reaction that involves the breaking of carbon-carbon double or triple bonds in the presence of oxidizing agents, such as ozone (O3). In alkynes, this process results in the formation of carboxylic acids or ketones, depending on the structure of the alkyne. The reaction typically occurs under controlled conditions, such as low temperatures, to prevent further reactions.

Alkynes and Their Structure

Alkynes are hydrocarbons that contain at least one carbon-carbon triple bond, characterized by the general formula CnH2n-2. The position of the triple bond significantly influences the reactivity and the products formed during reactions, including oxidative cleavage. Understanding the structure of alkynes is crucial for predicting the outcome of reactions and determining the resulting products.

Carboxylic Acids Formation

During oxidative cleavage of alkynes, the reaction typically yields carboxylic acids as products. In this case, the cleavage of the triple bond leads to the formation of a triacid and propionic acid, indicating that the original alkyne had specific substituents that contributed to these products. Recognizing the structure of the resulting acids helps in deducing the original alkyne's structure.

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Related Practice

Textbook Question

Show how you would synthesize the following carboxylic acids, using the indicated starting materials.

(a) oct-4-yne → butanoic acid

(b) trans-cyclodecene → decanedioic acid

Textbook Question

When treated with hydrogen and a platinum catalyst, an unknown compound X absorbs 5 equivalents of hydrogen to give n-butylcyclohexane. Treatment of X with an excess of ozone, followed by dimethyl sulfide and water, gives the following products:

Propose a structure for the unknown compound X. Is there any uncertainty in your structure?

Textbook Question

Predict the products of reaction of pent-1-yne with the following reagents.

g. cold, dilute KMnO₄

h. warm, concd. KMnO₄, NaOH

i. Na, liquid ammonia

Textbook Question

Oxidative cleavages can help to determine the positions of the triple bonds in alkynes.

(a) An unknown alkyne undergoes oxidative cleavage to give adipic acid and two equivalents of acetic acid. Propose a structure for the alkyne.

Textbook Question

Using cyclooctyne as your starting material, show how you would synthesize the following compounds. (Once you have shown how to synthesize a compound, you may use it as the starting material in any later parts of this problem.)

(g) cyclooctane-1,2-dione

Textbook Question

(i)

Textbook Question

Predict the product(s) you would expect from treatment of each compound with (1) dilute, neutral KMnO₄ and (2) warm basic KMnO₄, then dilute acid.

(d) 2-methylhex-3-yne

Textbook Question

Predict the product(s) you would expect from treatment of each compound with (1) dilute, neutral KMnO₄ and (2) warm basic KMnO₄, then dilute acid.

(e) cyclodecyne

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Oxidative cleavages can help to determine the positions of the triple bonds in alkynes. (b) An unknown alkyne undergoes oxidative cleavage to give the following triacid plus one equivalent of propionic acid. Propose a structure for the alkyne.

Key Concepts

Oxidative Cleavage

Alkynes and Their Structure

Carboxylic Acids Formation

Watch next

Oxidative cleavages can help to determine the positions of the triple bonds in alkynes.
(b) An unknown alkyne undergoes oxidative cleavage to give the following triacid plus one equivalent of propionic acid. Propose a structure for the alkyne.