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

9. Alkenes and Alkynes

Acetylide

Organic Chemistry

9. Alkenes and Alkynes

Acetylide

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2:00 minutes

Problem 120a(1)

Textbook Question

Draw the product of each of the following reactions:
1.

Verified step by step guidance

Step 1: Analyze the given reactants and reagents. The starting material is CH3CH2C≡CH (1-butyne), and the reaction involves two steps: (1) NaNH2 (sodium amide) and (2) CH3CH2Br (ethyl bromide). Sodium amide is a strong base that can deprotonate terminal alkynes, generating an acetylide ion.

Step 2: In the first step, NaNH2 deprotonates the terminal alkyne (CH3CH2C≡CH) to form the corresponding acetylide ion (CH3CH2C≡C⁻). This occurs because the terminal hydrogen on the alkyne is acidic and can be removed by a strong base.

Step 3: In the second step, the acetylide ion (CH3CH2C≡C⁻) acts as a nucleophile and undergoes an SN2 reaction with CH3CH2Br (ethyl bromide). The bromine atom in CH3CH2Br is a good leaving group, allowing the nucleophilic substitution to occur.

Step 4: The nucleophilic attack by the acetylide ion on the ethyl bromide results in the formation of a new carbon-carbon bond. The product of this reaction is an internal alkyne, specifically CH3CH2C≡CCH2CH3.

Step 5: Verify the structure of the product by ensuring that the reaction mechanism is consistent with the reagents used (deprotonation followed by nucleophilic substitution) and that the final product is an internal alkyne with the correct connectivity.

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Key Concepts

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

Alkyne Reactivity

Alkynes are hydrocarbons containing a carbon-carbon triple bond, which makes them highly reactive. In organic reactions, they can undergo various transformations, including nucleophilic substitutions and eliminations. Understanding the reactivity of alkynes is crucial for predicting the products of reactions involving them.

Nucleophilic Substitution

Nucleophilic substitution is a fundamental reaction mechanism in organic chemistry where a nucleophile replaces a leaving group in a molecule. In this case, sodium amide (NaNH2) acts as a strong nucleophile, facilitating the substitution of a hydrogen atom in the alkyne with a bromine atom from bromoethane (CH3CH2Br). This concept is essential for determining the final product of the reaction.

Reaction Mechanism

A reaction mechanism describes the step-by-step process by which reactants are converted into products. It includes the identification of intermediates, transition states, and the overall energy changes. Understanding the mechanism of the reaction between the alkyne and sodium amide is vital for predicting the structure of the final product and the pathway taken during the reaction.

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Related Practice

Textbook Question

Show the products of the following acetylide alkylation reactions. [Make sure your product has the correct number of carbons.]

(b)

Textbook Question

Calculate for the following acid–base reactions. Which is the best base to use to deprotonate acetylene and make the acetylide anion?

(c)

Textbook Question

Suggest reagents you might use to generate the product from the given reactant.

(b)

Textbook Question

A chemist is planning to synthesize 3-octyne by adding 1-bromobutane to the product obtained from the reaction of 1-butyne with sodium amide. Unfortunately, however, he forgot to order 1-butyne. How else can he prepare 3-octyne?

Textbook Question

Show how you might synthesize the following compounds, using acetylene and any suitable alkyl halides as your starting materials. If the compound given cannot be synthesized by this method, explain why.

d. 4-methylhex-2-yne

e. 5-methylhex-2-yne

f. cyclodecyne

Textbook Question

Show how the following compounds can be prepared, using ethyne as one of the starting materials:

3. 2-methyl-3-hexyn-2-ol

Textbook Question

Why is a cumulated diene not formed in the reaction shown above?

Textbook Question

A chemist attempted to do the following acetylide alkylation reaction but was unsuccessful in several attempts, producing only the original starting materials in each case. Explain why the reaction didn't work.

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Draw the product of each of the following reactions:1.

Key Concepts

Alkyne Reactivity

Nucleophilic Substitution

Reaction Mechanism

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Draw the product of each of the following reactions:
1.