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 Halogenation

Organic Chemistry

10. Addition Reactions

Alkyne Halogenation

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Problem 44f(ix)

Textbook Question

For the alkynes shows here, show the product(s) expected to form when treated under the following conditions: (ix) Br₂ (2 equiv.). If you expect two products, show both.
(f)

Verified step by step guidance

Step 1: Analyze the structure of the alkyne provided in the image. The molecule contains a terminal alkyne group (-C≡CH) attached to a complex cyclic structure with a nitrogen atom and a ketone functional group.

Step 2: Understand the reaction conditions. The treatment with Br₂ (2 equivalents) indicates that the alkyne will undergo halogenation. In this reaction, bromine molecules will add across the triple bond of the alkyne.

Step 3: Predict the first addition of Br₂. The triple bond will react with one equivalent of Br₂, resulting in the formation of a dibromoalkene intermediate. The bromine atoms will add anti to each other due to the mechanism of halogenation.

Step 4: Predict the second addition of Br₂. The dibromoalkene intermediate will react with the second equivalent of Br₂, leading to the formation of a tetrabromoalkane. The bromine atoms will add across the double bond, resulting in a saturated carbon chain with four bromine atoms.

Step 5: Consider stereochemistry and regioselectivity. Since the alkyne is terminal, the addition of bromine will occur without regioselectivity concerns. The stereochemistry of the final product will depend on the anti-addition mechanism during each step of halogenation.

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Key Concepts

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

Alkynes

Alkynes are hydrocarbons that contain at least one carbon-carbon triple bond. They are unsaturated compounds and are characterized by the general formula CnH2n-2. The presence of the triple bond significantly influences their reactivity, making them more reactive than alkenes and alkanes. Understanding the structure and reactivity of alkynes is crucial for predicting the products of chemical reactions involving these compounds.

Electrophilic Addition Reactions

Electrophilic addition reactions are a key type of reaction for unsaturated hydrocarbons, including alkynes. In these reactions, an electrophile reacts with the nucleophilic π bond of the alkyne, leading to the formation of new σ bonds. When treated with bromine (Br₂), for example, alkynes can undergo addition to form dibrominated products. Recognizing the mechanism of these reactions is essential for predicting the products formed under specific conditions.

Regioselectivity

Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others when multiple products are possible. In the case of alkynes reacting with bromine, the addition can occur at different positions, leading to different products. Understanding regioselectivity helps in predicting which isomer will be formed based on the stability of intermediates and the nature of the reactants involved.

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Related Practice

Textbook Question

Drawing on what you know about the stereochemistry of alkene addition reactions,

b. predict the configuration of the product of the reaction.

Textbook Question

Show how hex-1-yne might be converted to

d. 1,1,2,2-tetrabromohexane.

Textbook Question

Predict the product(s) that would result when the alkenes shown here are allowed to react under the following conditions: (v) 1. Hg(OAc)₂ , H₂O 2. NaBH₄

(b)

Textbook Question

Predict the products you would get when the following alkenes react under the following conditions: (i) H₂SO₄, H₂O and (ii) 1. Hg(OAc)₂, H₂O , 2. NaBH₄

(d)

Textbook Question

In Section 10.8.1, you learned that alkenes react more quickly with electrophiles than do the corresponding alkynes (k_alkene/k_alkyne > 1). Explain why there is a greater disparity in the alkene versus alkyne reactivity in the addition of HBr as compared to the addition of Br₂ [The rate data are not real, but are meant to illustrate a real trend.]

Textbook Question

α-Pinene is a terpene found in pine trees. Starting from geranyl diphosphate (a terpene), draw the arrow-pushing mechanism to produce α-pinene. Assume that an enzyme active site will provide whatever acids and bases you might need.

Textbook Question

Predict the products you would get when the following alkenes react under the following conditions: (i) H₂SO₄, H₂O and (ii) 1. Hg(OAc)₂, H₂O , 2. NaBH₄

(c)

Textbook Question

Predict the product(s) that would result when the alkenes shown here are allowed to react under the following conditions: (i) HBr; (ii) HCl; (iii) HBr, H₂O₂ (iv) H₂SO₄, H₂O (v) 1. Hg(OAc)_2, H₂O 2. NaBH₄ ; (vi) 1. BH₃ 2. H₂O₂, NaOH

(d)

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For the alkynes shows here, show the product(s) expected to form when treated under the following conditions: (ix) Br2 (2 equiv.). If you expect two products, show both.(f)

Key Concepts

Alkynes

Electrophilic Addition Reactions

Regioselectivity

Watch next

For the alkynes shows here, show the product(s) expected to form when treated under the following conditions: (ix) Br₂ (2 equiv.). If you expect two products, show both.
(f)