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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4:16 minutes

Problem 16c,d

Textbook Question

Predict the major product(s) of the following reactions:
c. cyclooctyne + 2 HBr
d. *hex-2-yne + 2 HCl

Verified step by step guidance

Step 1: Analyze the structure of the alkyne in each reaction. Cyclooctyne is a cyclic alkyne, while hex-2-yne is a linear alkyne with the triple bond located between carbons 2 and 3.

Step 2: Recall the mechanism of electrophilic addition of hydrogen halides (HX) to alkynes. The reaction proceeds in two steps: (1) addition of one molecule of HX to form a vinyl halide, and (2) addition of a second molecule of HX to form a geminal dihalide.

Step 3: For cyclooctyne + 2HBr, the first molecule of HBr adds across the triple bond, forming a vinyl bromide intermediate. The second molecule of HBr then adds to the same carbon, resulting in a geminal dibromide. The cyclic structure remains intact.

Step 4: For hex-2-yne + 2HCl, the first molecule of HCl adds across the triple bond, forming a vinyl chloride intermediate. The second molecule of HCl adds to the same carbon, resulting in a geminal dichloride. The major product will have the halogens attached to the same carbon (geminal position).

Step 5: Consider regioselectivity and Markovnikov's rule. In both reactions, the halogen will preferentially add to the more substituted carbon of the triple bond during each step, ensuring the major product follows Markovnikov's rule.

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Key Concepts

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

Electrophilic Addition Reactions

Electrophilic addition reactions involve the addition of electrophiles to nucleophiles, typically occurring in alkenes and alkynes. In the case of cyclooctyne and hex-2-yne, the triple bond acts as a nucleophile, reacting with the electrophilic hydrogen atoms from HBr or HCl. This process leads to the formation of more saturated products, often resulting in the addition of halogens across the multiple bonds.

Markovnikov's Rule

Markovnikov's Rule states that in the addition of HX to an alkene or alkyne, 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 reaction products, guiding the formation of major products when reacting compounds like hex-2-yne with HCl, where the more substituted carbon will preferentially bond with the halide.

Rearrangement and Stability of Carbocations

During electrophilic addition, carbocations may form as intermediates, and their stability is crucial for determining the reaction pathway. More stable carbocations, such as tertiary or secondary, are favored over less stable primary ones. Understanding the stability of these intermediates helps predict the major products of the reactions, as the pathway leading to the most stable carbocation will generally dominate.

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Related Practice

Textbook Question

Predict the alkyne and reactants you might use to make the following haloalkenes. [Providing the reactant and the reagent is how we start thinking about synthesis.]

(b)

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

Show how hex-1-yne might be converted to

f. 2,2-dibromohexane.

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.

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