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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6:00 minutes

Problem 54

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.

Verified step by step guidance

Step 1: Begin by selecting a terminal alkyne as the substrate for the experiment. For example, use 1-butyne or 1-hexyne, which are simple terminal alkynes.

Step 2: React the terminal alkyne with a hydrogen halide (H―X), such as HCl or HBr, under controlled conditions. Ensure the reaction is carried out in a solvent like dichloromethane or acetic acid to facilitate the addition reaction.

Step 3: Analyze the stereochemistry of the product formed using spectroscopic techniques such as Nuclear Magnetic Resonance (NMR) or Infrared (IR) spectroscopy. Look for evidence of anti addition (halogen and hydrogen added to opposite sides of the triple bond) or syn addition (halogen and hydrogen added to the same side).

Step 4: To confirm the stereochemistry further, use X-ray crystallography or compare the product to known stereoisomers if the product is crystalline. This will provide definitive structural information.

Step 5: Repeat the experiment with different hydrogen halides (e.g., HBr, HI) and compare the results to determine if the anti addition mechanism is consistent across various halides or if it varies depending on the halide used.

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Key Concepts

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

Alkynes and Their Reactivity

Alkynes are hydrocarbons containing at least one carbon-carbon triple bond. Their reactivity is significantly influenced by the nature of the triple bond, which can undergo various addition reactions. Understanding the structure and reactivity of terminal and internal alkynes is crucial, as terminal alkynes have a hydrogen atom attached to one end, affecting how they react with electrophiles like H-X.

Anti Addition Mechanism

Anti addition refers to a specific stereochemical outcome in addition reactions where substituents are added to opposite sides of a double or triple bond. This mechanism is important in determining the stereochemistry of the product formed from the reaction of alkynes with reagents like H-X. Recognizing how anti addition occurs can help predict the configuration of the resulting alkyl halide.

Experimental Design for Stereochemical Analysis

To resolve the dispute regarding anti addition in terminal alkynes, an experiment could involve the use of labeled reagents and stereospecific conditions. By performing the addition of H-X to a terminal alkyne and analyzing the product's stereochemistry using techniques like NMR or chiral chromatography, chemists can determine whether the addition occurs anti or not. This experimental approach provides empirical evidence to support or refute the claims of the chemists.

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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.]

(a)

Textbook Question

HBr and peroxides are also used to generate 1-bromo-1-alkenes. Suggest a starting reactant that would successfully undergo this reaction.

Textbook Question

Predict the major products resulting from the addition of one equivalent of HX to the following alkynes.

(b)

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

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