Textbook Question
Explain why the pKa of p-nitrophenol is 7.14, whereas the pKa of m-nitrophenol is 8.39.
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Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
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Bruice 8th EditionCh. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of BenzeneProblem 21c,d
Bruice 8th EditionCh. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of BenzeneProblem 21c,dChapter 9, Problem 21c,d
Which acid in each of the following pairs is stronger?
c. 
d. 
Verified step by step guidance1
Step 1: Analyze the molecular structures in pair (c). The first molecule (i) is cyclohexanecarboxylic acid, while the second molecule (ii) is cyclohexanecarboxylic acid with a ketone group attached to the ring. The ketone group is an electron-withdrawing group.
Step 2: Understand the effect of electron-withdrawing groups on acidity. Electron-withdrawing groups stabilize the conjugate base by delocalizing the negative charge, making the acid stronger.
Step 3: Compare the two molecules in pair (c). The ketone group in molecule (ii) increases the acidity of the carboxylic acid group compared to molecule (i), which lacks the electron-withdrawing ketone group.
Step 4: Analyze the molecular structures in pair (d). The first molecule (i) is cyclopentanecarboxylic acid, while the second molecule (ii) is cyclopentanecarboxylic acid with an amine group (-NH) attached to the ring. The amine group is an electron-donating group.
Step 5: Understand the effect of electron-donating groups on acidity. Electron-donating groups destabilize the conjugate base by increasing electron density, making the acid weaker. Therefore, molecule (i) is stronger than molecule (ii) in pair (d).
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acidity and pKa
Acidity refers to the ability of a compound to donate a proton (H+) in solution. The strength of an acid is often measured by its pKa value; lower pKa values indicate stronger acids. Understanding the relationship between structure and acidity is crucial, as factors like electronegativity and resonance can significantly influence a compound's ability to stabilize the negative charge of its conjugate base.
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07:45
Identifying pKa values
Resonance Stabilization
Resonance stabilization occurs when a molecule can be represented by multiple valid Lewis structures, allowing for the delocalization of electrons. This delocalization can stabilize the conjugate base formed after deprotonation, making the original acid stronger. In the context of the question, comparing the resonance effects in the given acid structures will help determine which acid is stronger.
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03:43The radical stability trend.
Inductive Effect
The inductive effect refers to the electron-withdrawing or electron-donating effects transmitted through sigma bonds in a molecule. Electronegative atoms or groups can stabilize the negative charge of a conjugate base through the inductive effect, enhancing acidity. Analyzing the presence of such groups in the acid structures presented will aid in assessing their relative strengths.
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01:47Understanding the Inductive Effect.
Related Practice
Textbook Question
For each of the following substituents, indicate whether it withdraws electrons inductively, donates electrons by hyperconjugation, withdraws electrons by resonance, or donates electrons by resonance.
d. NHCH3
e. OCH3
f. +N(CH3)3
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Textbook Question
Which acid in each of the following pairs is stronger?
e.
f.
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Textbook Question
What is the major product obtained from the addition of HBr to the following compound?
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Textbook Question
Which member of each pair is the stronger base?
c. phenolate ion or ethoxide ion
d. phenolate ion or acetate ion
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Textbook Question
For each of the following substituents, indicate whether it withdraws electrons inductively, donates electrons by hyperconjugation, withdraws electrons by resonance, or donates electrons by resonance.
a. Br
b. CH2CH3
c.
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