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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4:28 minutes

Problem 39d

Textbook Question

What is the major product of the reaction of 1 mol of propyne with each of the following reagents?
d. Br₂ (2 mol)/CH₂Cl₂

Verified step by step guidance

Identify the structure of propyne (CH≡C-CH3), which is an alkyne with a terminal triple bond.

Understand that Br2 in CH2Cl2 is a halogenation reagent, and in the presence of an alkyne, it will add bromine atoms across the triple bond.

Since 2 moles of Br2 are used, the reaction will proceed in two steps: (1) addition of 1 mole of Br2 to convert the triple bond into a double bond, and (2) addition of the second mole of Br2 to convert the double bond into a single bond.

Write the mechanism for the first step: The π electrons of the triple bond attack one Br2 molecule, forming a bromonium ion intermediate. A bromide ion (Br⁻) then attacks the intermediate, resulting in a dibromoalkene (CHBr=CHBr-CH3).

Write the mechanism for the second step: The π electrons of the double bond in the dibromoalkene attack the second Br2 molecule, forming another bromonium ion intermediate. A bromide ion (Br⁻) attacks again, leading to the final product, a tetrabromoalkane (CHBr2-CHBr2-CH3).

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Key Concepts

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

Alkyne Reactivity

Alkynes, such as propyne, are hydrocarbons with at least one carbon-carbon triple bond. They are more reactive than alkenes due to the presence of this triple bond, which can undergo various addition reactions. Understanding the reactivity of alkynes is crucial for predicting the products of their reactions with different reagents.

Electrophilic Addition

Electrophilic addition is a fundamental reaction mechanism in organic chemistry where an electrophile reacts with a nucleophile, leading to the formation of a more stable product. In the case of propyne reacting with bromine (Br2), the triple bond acts as a nucleophile, attacking the electrophilic bromine, resulting in the addition of bromine across the triple bond.

Bromination of Alkynes

Bromination of alkynes involves the addition of bromine to the carbon-carbon triple bond, typically resulting in a dibrominated product. When 2 moles of Br2 are used, the reaction can lead to the formation of a vicinal dibromide, where bromine atoms are added to adjacent carbon atoms. This process is important for understanding how alkynes can be transformed into more complex molecules.

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Related Practice

Textbook Question

Predict the products of reaction of pent-1-yne with the following reagents.

d. H₂, Pd/BaSO₄, quinoline

e. 1 equivalent of Br₂

f. 2 equivalents of Br₂

Textbook Question

What stereoisomers are obtained when 2-butyne undergoes each of the following reaction sequences?

c. 1. Cl₂/CH₂Cl₂ 2. Br₂/CH₂Cl₂

Textbook Question

What reagents should be used to carry out the following syntheses?

Multiple Choice

Predict the major, organic product of the following reaction.

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.

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What is the major product of the reaction of 1 mol of propyne with each of the following reagents? d. Br2 (2 mol)/CH2Cl2

Key Concepts

Alkyne Reactivity

Electrophilic Addition

Bromination of Alkynes

Watch next

What is the major product of the reaction of 1 mol of propyne with each of the following reagents?
d. Br₂ (2 mol)/CH₂Cl₂