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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3:36 minutes

Problem 44c(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.
(c)

Verified step by step guidance

Identify the alkyne structure in the given problem. Alkynes are hydrocarbons containing a carbon-carbon triple bond (C≡C). Note that the reaction involves Br₂ (bromine) in 2 equivalents, which means the reaction will proceed in two steps.

Understand the reaction mechanism: When an alkyne reacts with Br₂, the first equivalent of bromine adds across the triple bond, converting it into a dibromoalkene (a double bond with two bromine atoms attached). The second equivalent of bromine then reacts with the dibromoalkene to form a tetrabromoalkane (a single bond with four bromine atoms attached).

Write the reaction for the first equivalent of Br₂: The triple bond (C≡C) undergoes an electrophilic addition reaction with Br₂, forming a trans-dibromoalkene. Represent this intermediate product using the correct chemical structure.

Write the reaction for the second equivalent of Br₂: The trans-dibromoalkene reacts with another molecule of Br₂, resulting in the addition of two more bromine atoms across the double bond. This forms a tetrabromoalkane as the final product. Represent this final product using the correct chemical structure.

If stereochemistry is relevant, ensure that you indicate the stereochemical outcomes (e.g., anti-addition for the first step). If two products are possible due to symmetry or regioselectivity, clearly show both products and explain why they form.

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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 (C≡C). They are unsaturated compounds and are generally more reactive than alkenes and alkanes due to the presence of this triple bond. 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 occur when an electrophile reacts with a nucleophile, leading to the formation of a more saturated product. In the case of alkynes, the triple bond acts as a nucleophile, allowing electrophiles like bromine (Br₂) to add across the triple bond. This reaction typically results in the formation of dibrominated products when two equivalents of bromine are used.

Regioselectivity and Stereochemistry

Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others, while stereochemistry involves the spatial arrangement of atoms in molecules. When alkynes react with bromine, the addition can lead to different products based on how the bromine atoms add to the carbon atoms of the triple bond, resulting in both regioisomers and potential stereoisomers, depending on the reaction conditions.

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Related Practice

Textbook Question

Answer Problem 39 , parts a–h, using 2-butyne as the starting material instead of propyne.

c. Br₂ (1 mol)/CH₂Cl₂

Textbook Question

What is the major product of the reaction of 1 mol of propyne with each of the following reagents?

c. Br₂ (1 mol)/CH₂Cl₂

Textbook Question

In the addition of just 1 mole of bromine to 1 mole of hex-1-yne, should the hex-1-yne be added to a bromine solution or should the bromine be added to the hex-1-yne? Explain your answer.

Textbook Question

For the alkynes shows here, show the product(s) expected to form when treated under the following conditions: (viii) Cl₂ (1 equiv.). If you expect two products, show both.

(c)

Textbook Question

Trans addition is heavily favored for the addition of Br₂ and Cl₂ to alkynes. With chlorination, however, more of the syn addition product is formed. Rationalize this fact in light of your answer to Assessments 10.50 and 10.51.

Textbook Question

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

a. write the mechanism for the reaction of 2-butyne with one equivalent of Br₂.

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.

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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.(c)

Key Concepts

Alkynes

Electrophilic Addition Reactions

Regioselectivity and Stereochemistry

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.
(c)