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

Previous problemNext problem

Problem 15a

Textbook Question

Calculate K_eq for the following acid–base reactions. Which is the best base to use to deprotonate acetylene and make the acetylide anion?
(a) HO^- + H―C ≡ C―H ⇌ ^-C ≡ C―H + H₂O

Verified step by step guidance

Step 1: Understand the problem. The goal is to determine whether hydroxide (HO⁻) is a strong enough base to deprotonate acetylene (H―C≡C―H) and form the acetylide anion (⁻C≡C―H). This involves comparing the acidities of the reactants and products using their pKa values.

Step 2: Recall the concept of pKa. The pKa value is a measure of the acidity of a compound. A lower pKa indicates a stronger acid. The equilibrium of an acid-base reaction favors the side with the weaker acid (higher pKa).

Step 3: Identify the pKa values of the relevant species. Acetylene (H―C≡C―H) has a pKa of approximately 25, while water (H₂O), the conjugate acid of hydroxide (HO⁻), has a pKa of approximately 15.7.

Step 4: Compare the pKa values. Since acetylene has a higher pKa (25) than water (15.7), acetylene is a weaker acid than water. This means the equilibrium will not favor the formation of the acetylide anion (⁻C≡C―H) when hydroxide is used as the base.

Step 5: Conclude that hydroxide (HO⁻) is not a strong enough base to deprotonate acetylene effectively. A stronger base, such as sodium amide (NaNH₂, conjugate acid NH₃ with pKa ~38), would be required to deprotonate acetylene and form the acetylide anion.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Play a video:

Was this helpful?

Key Concepts

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

Acidity and Basicity

Acidity refers to the tendency of a compound to donate protons (H⁺), while basicity is the ability to accept protons. In organic chemistry, the strength of an acid is often measured by its pKa value; lower pKa values indicate stronger acids. Understanding the relative strengths of acids and bases is crucial for predicting the outcome of acid-base reactions.

Acetylide Anion

The acetylide anion (C≡C⁻) is formed when acetylene (H―C≡C―H) is deprotonated. This anion is a strong nucleophile and is important in organic synthesis, particularly in reactions involving carbon-carbon bond formation. Identifying a suitable base to generate the acetylide anion is essential for various synthetic applications.

Strong Bases for Deprotonation

To deprotonate a weak acid like acetylene, a strong base is required. Common strong bases include alkoxides (like NaO⁻) and hydrides (like NaH). The choice of base affects the efficiency of the deprotonation process, and understanding the relative strength of potential bases is key to selecting the best one for generating the acetylide anion.

Watch next

Master Understanding how to convert terminal alkynes to alkynides. with a bite sized video explanation from Johnny

Start learning

Related Videos

Related Practice

Textbook Question

Suggest an acetylide ion and a carbonyl that might be used to make the following products.

Textbook Question

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

(d)

Textbook Question

The introduction of elimination reactions provides a second way to synthesize alkynes in a two-step process starting with an alkene. Suggest a mechanism for both steps of this process.

Textbook Question

When the reaction scheme in Assessment 12.63 is done on a monosubstituted alkene, at least three equivalents of base are needed. Reacting the product of step 2 with D–Cl (D is an isotope of H) incorporates deuterium at the terminal carbon. Explain these two observations.

Textbook Question

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

(b) H₂N^- + H―C ≡ C―H ⇌ ^-C ≡ C―H + H₃N

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)

Show more practices

Download the Mobile app

Privacy

Do not sell my personal information

Accessibility

Patent notice

Sitemap

Calculate Keq for the following acid–base reactions. Which is the best base to use to deprotonate acetylene and make the acetylide anion?(a) HO- + H―C ≡ C―H ⇌ -C ≡ C―H + H2O

Key Concepts

Acidity and Basicity

Acetylide Anion

Strong Bases for Deprotonation

Watch next

Calculate K_eq for the following acid–base reactions. Which is the best base to use to deprotonate acetylene and make the acetylide anion?
(a) HO^- + H―C ≡ C―H ⇌ ^-C ≡ C―H + H₂O