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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4:06 minutes

Problem 4b

Textbook Question

Predict the product of the following reactions.
(b)

Verified step by step guidance

Step 1: Identify the type of reaction. The reaction involves hydrogen gas (H₂) and platinum (Pt), which indicates a catalytic hydrogenation reaction. This type of reaction typically reduces double bonds (alkenes) to single bonds (alkanes).

Step 2: Locate the functional groups in the molecule. The molecule contains a double bond (alkene), hydroxyl group (-OH), bromine atoms (Br), and an ethyl group (-CH₂CH₃). The double bond is the primary target for hydrogenation.

Step 3: Predict the effect of hydrogenation. The double bond will be reduced to a single bond, resulting in the addition of two hydrogen atoms to the carbons involved in the double bond. The stereochemistry of the product will depend on the reaction conditions, but catalytic hydrogenation typically leads to syn addition (both hydrogens added to the same face of the molecule).

Step 4: Consider the stereochemistry of the molecule. The hydroxyl group and bromine atoms are already stereochemically defined. The addition of hydrogen atoms will not affect these groups but will influence the stereochemistry of the newly formed single bond.

Step 5: Draw the product structure. Replace the double bond with a single bond and add two hydrogen atoms to the carbons that were part of the double bond. Ensure the stereochemistry is consistent with syn addition, and retain the original stereochemistry of the hydroxyl and bromine groups.

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Key Concepts

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

Hydrogenation

Hydrogenation is a chemical reaction that involves the addition of hydrogen (H2) to an unsaturated compound, typically alkenes or alkynes, to convert them into saturated hydrocarbons. This process often requires a catalyst, such as platinum (Pt), palladium (Pd), or nickel (Ni), to facilitate the reaction. In the context of the provided reaction, hydrogenation will convert the alkyne into an alkene or alkane, depending on the extent of hydrogenation.

Bromination

Bromination is the addition of bromine (Br2) to a compound, which can occur in various ways, including electrophilic addition to alkenes or alkynes. In the reaction shown, the presence of bromine atoms indicates that the compound has undergone bromination, which can influence the reactivity and stability of the resulting product after hydrogenation. Understanding the positioning of bromine substituents is crucial for predicting the final product.

Regioselectivity

Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others when multiple possibilities exist. In the context of the reaction shown, the regioselectivity will determine which carbon atoms in the alkyne will be hydrogenated and how the bromine substituents will affect the final product. This concept is essential for predicting the outcome of reactions involving multiple functional groups or substituents.

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