Textbook Question
For each indicated proton, suggest an approximate pKa value from Table 4.5. Rationalize your choice.
(d)
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Ch. 4 - Acids and Bases: Electron Flow
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
Chapter 3, Problem 40d
For the bases shown, draw the conjugate acid and identify a pKa value from Table 4.5 that would help you accurately estimate its stability.
(d) 
Verified step by step guidance1
Step 1: Identify the base shown in the image. The structure represents an isopropyl anion (CH₃)₂CH⁻, which is a negatively charged carbon atom bonded to two methyl groups and one hydrogen atom.
Step 2: To draw the conjugate acid, add a proton (H⁺) to the base. This will neutralize the negative charge on the carbon atom, resulting in isopropane (CH₃)₂CH₂.
Step 3: Recall that the conjugate acid of a base has a pKₐ value that reflects its acidity. The pKₐ value can be found in Table 4.5, which lists the pKₐ values of common acids. For isopropane, the pKₐ of its conjugate acid is approximately 50, indicating it is a very weak acid.
Step 4: Use the pKₐ value to estimate the stability of the base. A high pKₐ value (like 50) suggests that the conjugate acid is very stable, and the base (isopropyl anion) is relatively unstable.
Step 5: Summarize the findings: The conjugate acid of the isopropyl anion is isopropane, and its pKₐ value of approximately 50 indicates that the base is unstable and the conjugate acid is highly stable.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Conjugate Acids and Bases
In acid-base chemistry, a conjugate acid is formed when a base accepts a proton (H⁺). Understanding this concept is crucial for predicting the behavior of substances in reactions. For example, when ammonia (NH₃) acts as a base, it can accept a proton to form its conjugate acid, ammonium (NH₄⁺). This relationship helps in determining the strength of acids and bases.
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Equilibrium constant and conjugates.
pKₐ and Acid Strength
pKₐ is a quantitative measure of the strength of an acid in solution, with lower values indicating stronger acids. It is derived from the acid dissociation constant (Kₐ), which reflects the extent to which an acid donates protons. Understanding pKₐ values is essential for comparing the stability of conjugate acids and bases, as they provide insight into the equilibrium position of acid-base reactions.
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Stability of Conjugate Acids
The stability of a conjugate acid is influenced by factors such as electronegativity, resonance, and inductive effects. A more stable conjugate acid corresponds to a weaker base, as it is less likely to donate a proton. Evaluating the stability of conjugate acids helps in predicting the direction of acid-base reactions and understanding the relative strengths of the corresponding bases.
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Related Practice
Textbook Question
Without using pKa values, pick out the more reactive (least stable) base in each pair. Explain your answer.
(a)
1036
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Textbook Question
For the bases shown, draw the conjugate acid and identify a pKa value from Table 4.5 that would help you accurately estimate its stability.
(b)
1131
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Textbook Question
For the bases shown, draw the conjugate acid and identify a pKa value from Table 4.5 that would help you accurately estimate its stability.
(c)
873
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Textbook Question
Without using pKa values, pick out the more acidic compound in each pair. Explain your answer.
(a)
1196
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Textbook Question
For the bases shown, draw the conjugate acid and identify a pKa value from Table 4.5 that would help you accurately estimate its stability.
(e)
1320
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