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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4:48 minutes

Problem 44c(viii)

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)

Verified step by step guidance

Identify the alkyne structure provided in the problem. Alkynes are hydrocarbons containing a carbon-carbon triple bond (C≡C). Determine if the alkyne is terminal (triple bond at the end of the chain) or internal (triple bond within the chain).

Understand the reagent and reaction conditions: Cl₂ (1 equiv.) indicates that one equivalent of chlorine (Cl₂) will react with the alkyne. This is a halogenation reaction, where the alkyne reacts with halogens to form dihaloalkenes.

Recognize the mechanism: The reaction proceeds via an anti-addition mechanism. The Cl₂ molecule adds across the triple bond, breaking one π-bond of the alkyne and forming a double bond (C=C). The two chlorine atoms attach to the carbons of the former triple bond in a trans (anti) configuration.

Determine the stereochemistry and regioselectivity: Since the reaction is anti-addition, the two chlorine atoms will be added to opposite sides of the double bond. If the alkyne is symmetrical, only one product will form. If the alkyne is asymmetrical, two stereoisomers (E and Z) may form.

Draw the product(s): For a symmetrical alkyne, draw the single dihaloalkene product with the chlorine atoms in a trans configuration. For an asymmetrical alkyne, draw both possible stereoisomers (E and Z) of the dihaloalkene, showing the placement of the chlorine atoms and the double bond.

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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 generally more reactive than alkenes and alkanes due to the presence of the triple bond. This reactivity allows them to undergo various addition reactions, including halogenation, where halogens like Cl₂ can add across the triple bond.

Halogenation of Alkynes

Halogenation is a reaction where halogens, such as chlorine (Cl₂), react with unsaturated hydrocarbons. In the case of alkynes, the addition of Cl₂ can lead to the formation of dihaloalkenes or even saturated compounds, depending on the conditions. When one equivalent of Cl₂ is added to an alkyne, it typically results in the formation of a vinyl halide and a potential further reaction product.

Regioselectivity

Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others when multiple products are possible. In the halogenation of alkynes, the position where the halogen adds can lead to different products, and understanding the regioselectivity helps predict which isomer will be favored. This concept is crucial for determining the expected products when treating alkynes with halogens.

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Related Practice

Textbook Question

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

d. Br₂ (2 mol)/CH₂Cl₂

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: (ix) Br₂ (2 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.

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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)

Key Concepts

Alkynes

Halogenation of Alkynes

Regioselectivity

Watch next

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)