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 Hydrohalogenation

Organic Chemistry

10. Addition Reactions

Alkyne Hydrohalogenation

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1:43 minutes

Problem 18f

Textbook Question

Show how hex-1-yne might be converted to
f. 2,2-dibromohexane.

Verified step by step guidance

Step 1: Begin with hex-1-yne, which is an alkyne with a triple bond between the first and second carbons in a six-carbon chain. The goal is to convert this alkyne into 2,2-dibromohexane, which is an alkane with two bromine atoms attached to the second carbon.

Step 2: Perform a hydrohalogenation reaction using excess HBr (hydrogen bromide). In the presence of excess HBr, the alkyne undergoes two successive additions of HBr. The first addition converts the triple bond into a double bond, forming a bromoalkene. The second addition converts the double bond into a single bond, forming a dibromoalkane.

Step 3: Apply Markovnikov's rule during the hydrohalogenation reaction. According to Markovnikov's rule, the hydrogen atom from HBr will add to the carbon with more hydrogen atoms (the terminal carbon in this case), while the bromine atom will add to the carbon with fewer hydrogen atoms (the second carbon). This ensures that both bromine atoms end up on the second carbon.

Step 4: Verify the structure of the product. After the reaction, the resulting compound should be 2,2-dibromohexane, where the second carbon in the chain is bonded to two bromine atoms, and the rest of the chain remains saturated with single bonds.

Step 5: Ensure reaction conditions are appropriate. The reaction typically requires a polar solvent like acetic acid or dichloromethane to facilitate the addition of HBr. Excess HBr ensures complete conversion of the alkyne to the dibromoalkane.

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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 characterized by a carbon-carbon triple bond, which makes them highly reactive. This reactivity allows them to undergo various addition reactions, where reagents can add across the triple bond. Understanding how alkynes react is crucial for converting them into other compounds, such as alkenes or alkanes, which can then be further modified.

Halogenation

Halogenation is a chemical reaction where halogens (like bromine) are added to a compound. In the case of converting hex-1-yne to 2,2-dibromohexane, the addition of bromine across the triple bond will first yield a dibromoalkene. This step is essential for introducing the bromine atoms at the desired positions in the final product.

Markovnikov's Rule

Markovnikov's Rule states that in the addition of HX (where X is a halogen) to an alkene, the hydrogen atom will attach to the carbon with the greater number of hydrogen atoms already attached. This principle helps predict the regioselectivity of the halogenation reaction, ensuring that the bromine atoms are added to the more substituted carbon, leading to the formation of 2,2-dibromohexane.

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Related Practice

Textbook Question

The addition of H―X to alkynes has been shown to occur predominately via anti addition:

Two chemists disagreed on whether or not anti addition would happen on terminal alkynes as well. Suggest an experiment through which you could resolve this dispute.

Textbook Question

What is the major product obtained from the reaction of each of the following compounds with excess HCl?

c. CH₃CH₂C☰CCH₂CH₂CH₃

Textbook Question

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

a. HBr (1 mol)

b. HBr (2 mol)

Textbook Question

Predict the major product(s) of the following reactions:

c. cyclooctyne + 2 HBr

d. *hex-2-yne + 2 HCl

Textbook Question

Using hex-1-ene 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.)

a. 1,2-dibromohexane

b. hex-1-yne

c. 2,2-dibromohexane

Textbook Question

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

a. 1 equivalent of HCl

b. 2 equivalents of HCl

c. excess H₂, Ni

Multiple Choice

Predict the major, organic product of the following reaction.

Textbook Question

Predict the major product(s) of the following reactions: