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

Halogenation

Organic Chemistry

10. Addition Reactions

Halogenation

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6:27 minutes

Problem 27b

Textbook Question

What is the major product of each of the following reactions, assuming that one equivalent of each reagent is used in each reaction?
b.

Verified step by step guidance

Analyze the structure of the starting compound: The molecule contains both a terminal alkyne (≡C) and a terminal alkene (C=C). These functional groups are reactive toward bromine (Br₂).

Understand the reaction mechanism: Bromine reacts with alkenes and alkynes via electrophilic addition. For one equivalent of Br₂, the reaction will preferentially occur at the more reactive site, which is typically the alkene due to its higher electron density compared to the alkyne.

Predict the product at the alkene: The addition of Br₂ to the alkene will result in the formation of a vicinal dibromide (two bromine atoms added across the double bond). The stereochemistry of the addition is anti, meaning the bromine atoms will add to opposite sides of the double bond.

Consider the alkyne: Since only one equivalent of Br₂ is used, the alkyne remains unreacted in this case. The alkyne is less reactive than the alkene under these conditions.

Combine the results: The major product will have the alkene converted into a vicinal dibromide, while the alkyne remains intact. The structure of the product will reflect this selective reactivity.

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Key Concepts

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

Alkynes and Their Reactivity

Alkynes are hydrocarbons that contain at least one carbon-carbon triple bond. They are generally more reactive than alkenes due to the presence of this triple bond, which can undergo various reactions, including halogenation. In halogenation, alkynes react with halogens (like Br2) to form dihaloalkenes or tetrahaloalkanes, depending on the conditions and the number of equivalents of halogen used.

Halogenation Mechanism

The halogenation of alkynes typically proceeds through an electrophilic addition mechanism. Initially, the triple bond acts as a nucleophile, attacking a halogen molecule, leading to the formation of a cyclic halonium ion intermediate. This intermediate is then attacked by a halide ion, resulting in the formation of a vicinal dibromide product. Understanding this mechanism is crucial for predicting the major product of the reaction.

Regioselectivity in Reactions

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 halogenation of alkynes, the regioselectivity can be influenced by the structure of the alkyne and the conditions of the reaction. For example, terminal alkynes may lead to different products compared to internal alkynes, affecting the final product distribution.

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Related Practice

Textbook Question

Predict the major products of the following reactions, and give the structures of any intermediates. Include stereochemistry where appropriate.

(b)

Textbook Question

Propose mechanisms and predict the major products of the following reactions. Include stereochemistry where appropriate.

(d) (Z)-dec-3-ene + Br₂ in CCl₄

Problem-Solving Hint: Models may be helpful whenever stereochemistry is involved. Write complete structures, including all bonds and charges, when writing mechanisms.

Textbook Question

Give mechanisms to account for the stereochemistry of the products observed from the addition of bromine to cis- and trans-but-2-ene (Figure 8-5). Why are two products formed from the cis isomer but only one from the trans? (Making models will be helpful.)

Textbook Question

Using 1,2-dimethylcyclohexene 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.) If a chiral product is shown, assume that it is part of a racemic mixture.

(c)

Textbook Question

Predict the product(s) that would result when the alkenes are allowed to react under the following conditions: (i) Br₂

(d)

Textbook Question

Predict the product(s) that would result when the alkenes are allowed to react under the following conditions: (ii) Cl₂

(d)

Textbook Question

Predict the product(s) that would result when the alkenes are allowed to react under the following conditions: (i) Br₂

(h)

Textbook Question

Predict the product(s) that would result when the alkenes are allowed to react under the following conditions: (ii) Cl₂

(h)

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What is the major product of each of the following reactions, assuming that one equivalent of each reagent is used in each reaction? b.

Key Concepts

Alkynes and Their Reactivity

Halogenation Mechanism

Regioselectivity in Reactions

Watch next

What is the major product of each of the following reactions, assuming that one equivalent of each reagent is used in each reaction?
b.