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
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Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471
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Table of contents
- Ch. 2 - General Chemistry Translated: Finding the Electrons114
- Ch. 3 - Alkanes and Cycloalkanes: Properties and Conformational Analysis109
- Ch. 4 - Acids and Bases: Electron Flow144
- Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics118
- Ch. 6 - Stereoisomerism: Arrangement of Atoms in Space112
- Ch. 7 - Principles of Green (Organic) Chemistry3
- Ch. 8 - Alkenes I: Properties and Electrophilic Additions158
- Ch. 9 - Alkenes II: Oxidation and Reduction150
- Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions101
- Ch. 11 - Properties and Synthesis of Alkyl Halides: Radical Reactions108
- Ch. 12 - Substitution and Elimination: Reactions of Haloalkanes172
- Ch. 13 - Alcohols, Ethers and Related Compounds: Substitution and Elimination239
- Ch. 14 - Structural Identification I: Infrared Spectroscopy and Mass Spectrometry54
- Ch. 15 - Structural Identification II: Nuclear Magnetic Resonance Spectroscopy93
- Ch. 16 - Metals in Organic Chemistry48
- Ch. 17 - Carbonyl Addition Reactions: Aldehydes and Ketones45
- Ch. 18 - Nucleophilic Acyl Substitution I: Carboxylic Acids18
- Ch. 19 - Nucleophilic Acyl Substitution II: Carboxylic Acid Derivatives39
- Ch. 20 - Enolates: Carbonyl Addition and Substitution13
- Ch. 21 - Conjugated Systems I: Stability and Addition Reactions56
- Ch. 22 - Conjugated Systems II: Pericyclic Reactions54
- Ch. 23 - Benzene I: Aromatic Stability and Substitution Reactions64
- Ch. 24 - Benzene II: Reactions Influenced by the Aromatic Ring62
- Ch. 25 - Amines: Structure, Reactions, and Synthesis27
- Ch. 26 - Amino Acids, Proteins, and Peptide Synthesis9
- Ch. 27 - Carbohydrates, Nucleic Acids, and Lipids54
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
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Mullins 1st EditionCh. 10 - Alkynes: Electrophilic Addition and Redox ReactionsProblem 17a
Mullins 1st EditionCh. 10 - Alkynes: Electrophilic Addition and Redox ReactionsProblem 17aChapter 9, Problem 17a
Estimate the Keq for the following reactions based on the stability of the anions involved.
(a) 
Verified step by step guidance1
Analyze the reaction: The reaction involves the deprotonation of an alkyne to form an acetylide anion and the protonation of a ketone to form an alkoxide anion. The equilibrium constant (K_eq) depends on the relative stability of the anions formed.
Step 1: Evaluate the stability of the acetylide anion. Acetylide anions are stabilized by the sp hybridization of the carbon atom bearing the negative charge. The sp hybridization results in a high electronegativity, making the acetylide anion relatively stable.
Step 2: Evaluate the stability of the alkoxide anion. Alkoxide anions are less stable compared to acetylide anions because the oxygen atom bearing the negative charge is sp3 hybridized, which is less electronegative than sp hybridized carbon.
Step 3: Compare the acidity of the conjugate acids. The conjugate acid of the acetylide anion is the terminal alkyne, which has a pKa of approximately 25. The conjugate acid of the alkoxide anion is the ketone, which has a pKa of approximately 20. Since the terminal alkyne is less acidic, its conjugate base (acetylide anion) is more stable.
Step 4: Conclude the direction of equilibrium. Since the acetylide anion is more stable than the alkoxide anion, the equilibrium will favor the formation of the acetylide anion. Therefore, K_eq is expected to be greater than 1, favoring the products.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acid-Base Equilibrium
Acid-base equilibrium refers to the balance between acids and bases in a chemical reaction. In this context, it involves the transfer of protons (H+) between species, leading to the formation of anions. The position of equilibrium is influenced by the relative strengths of the acids and bases involved, which can be assessed through their dissociation constants (K_a and K_b).
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Stability of Anions
The stability of anions is a crucial factor in determining the favorability of a reaction. More stable anions are less likely to re-accept protons, thus favoring the formation of products. Factors affecting anion stability include electronegativity, resonance, and the size of the atom bearing the negative charge. A more stable anion corresponds to a larger equilibrium constant (K_eq) for the reaction.
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Equilibrium Constant (K_eq)
The equilibrium constant (K_eq) quantifies the ratio of the concentrations of products to reactants at equilibrium for a given reaction. A higher K_eq indicates that the products are favored, while a lower K_eq suggests that reactants are favored. In acid-base reactions, K_eq can be estimated based on the relative stabilities of the anions formed, with more stable anions leading to larger K_eq values.
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Related Practice
Textbook Question
Draw a transition state for the following substitution reaction.
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Textbook Question
Using pKa values, calculate an approximate Keq value for the following substitution reaction.
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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)
1
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Textbook Question
Estimate the Keq for the following reactions based on the stability of the anions involved.
(c)
1
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Textbook Question
Estimate the Keq for the following reactions based on the stability of the anions involved.
(b)
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