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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2:14 minutes

Problem 18d

Textbook Question

Show how hex-1-yne might be converted to
d. 1,1,2,2-tetrabromohexane.

Verified step by step guidance

Identify the starting material and the target product. The starting material is hex-1-yne, which is an alkyne, and the target product is 1,1,2,2-tetrabromohexane, which is a fully saturated alkane with four bromine atoms attached to the first and second carbons.

Recognize that the reaction involves the addition of bromine (Br₂) to the alkyne. This process occurs in two steps: (1) addition of bromine to the triple bond to form a dibromoalkene, and (2) further addition of bromine to the double bond to form the tetrabromoalkane.

In the first step, treat hex-1-yne with one equivalent of bromine (Br₂) in an inert solvent like CCl₄. This will result in the formation of 1,2-dibromohex-1-ene. The bromine atoms will add across the triple bond in an anti-addition manner, forming a trans-dibromoalkene.

In the second step, treat the 1,2-dibromohex-1-ene with another equivalent of bromine (Br₂) in the same solvent. This will result in the addition of two more bromine atoms across the double bond, forming 1,1,2,2-tetrabromohexane. The addition will again proceed via anti-addition.

Finally, confirm the structure of the product. The resulting compound, 1,1,2,2-tetrabromohexane, will have two bromine atoms attached to the first carbon and two bromine atoms attached to the second carbon, with the rest of the molecule being a fully saturated alkane chain.

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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 hex-1-yne, are hydrocarbons containing a carbon-carbon triple bond. This triple bond makes them highly reactive, particularly in addition reactions. Understanding how alkynes can undergo reactions with halogens is crucial for converting them into more complex molecules, such as tetrabromo derivatives.

Halogenation

Halogenation is a chemical reaction where halogens (like bromine) are added to a compound. In the case of alkynes, this process can lead to the formation of vicinal dibromides. For hex-1-yne to be converted to 1,1,2,2-tetrabromohexane, multiple halogenation steps are required, which involve the addition of bromine across the triple bond.

Stereochemistry

Stereochemistry refers to the spatial arrangement of atoms in molecules and how this affects their chemical behavior. In the conversion of hex-1-yne to 1,1,2,2-tetrabromohexane, understanding the stereochemical outcomes of halogenation is important, as the product will have specific stereochemical configurations that influence its properties and reactivity.

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Related Practice

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.

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

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)

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.]

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Show how hex-1-yne might be converted tod. 1,1,2,2-tetrabromohexane.

Key Concepts

Alkyne Reactivity

Halogenation

Stereochemistry

Watch next

Show how hex-1-yne might be converted to
d. 1,1,2,2-tetrabromohexane.