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

Hydrogenation of Alkynes

Organic Chemistry

9. Alkenes and Alkynes

Hydrogenation of Alkynes

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2:20 minutes

Problem 64d

Textbook Question

Hydration of alkynes (via oxymercuration) gives good yields of single compounds only with symmetrical or terminal alkynes. Show what the products would be from hydration of each compound.
d. cyclodecyne

Verified step by step guidance

Identify the reaction type: The problem involves the hydration of an alkyne via oxymercuration. This reaction adds water (H₂O) across the triple bond of the alkyne in the presence of a mercuric ion catalyst (commonly HgSO₄) and an acid (H₂SO₄). The product is typically a ketone due to tautomerization of the enol intermediate.

Analyze the structure of cyclodecyne: Cyclodecyne is a cyclic alkyne with a triple bond in a 10-membered ring. Since it is an internal alkyne (not terminal), the hydration will not produce a single product but rather a mixture of ketones due to the lack of symmetry.

Determine the regioselectivity: In the hydration of internal alkynes, the addition of water is not regioselective because both carbons of the triple bond are equally substituted. This means the enol intermediate can form on either carbon of the triple bond, leading to two possible ketones after tautomerization.

Write the reaction mechanism: (1) The alkyne reacts with Hg²⁺ to form a mercurinium ion intermediate. (2) Water attacks the more electrophilic carbon of the triple bond, leading to the formation of an enol. (3) The enol undergoes acid-catalyzed tautomerization to form a ketone. Repeat this process for both possible enol intermediates to identify the two ketone products.

Draw the products: The two ketones will differ based on which carbon of the triple bond the water adds to. In cyclodecyne, this results in two ketones with the carbonyl group located at different positions within the 10-membered ring.

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Key Concepts

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

Hydration of Alkynes

Hydration of alkynes involves the addition of water (H2O) across the triple bond of an alkyne, typically in the presence of an acid catalyst. This reaction can lead to the formation of enols, which can subsequently tautomerize to form ketones or aldehydes. The regioselectivity of this reaction is influenced by the structure of the alkyne, particularly whether it is symmetrical or terminal.

Oxymercuration-Demercuration

Oxymercuration-demercuration is a two-step reaction used to hydrate alkenes and alkynes. In the first step, mercuric acetate reacts with the alkyne to form a mercurial intermediate, which is then treated with water to yield an alcohol. The second step involves the reduction of the mercurial compound to remove mercury, resulting in the formation of the final alcohol product. This method is particularly useful for achieving Markovnikov selectivity.

Symmetrical vs. Terminal Alkynes

Symmetrical alkynes have identical substituents on both ends of the triple bond, leading to a single product upon hydration. In contrast, terminal alkynes have a hydrogen atom at one end, allowing for the formation of different products depending on the regioselectivity of the reaction. Understanding the distinction between these types of alkynes is crucial for predicting the outcome of hydration reactions, especially in terms of product distribution.

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