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 21e,f
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 21e,fChapter 9, Problem 21e,f
Which acid in each of the following pairs is stronger?
e. 
f. 
Verified step by step guidance1
Step 1: Analyze the acids in pair A. The first acid (i) is 2,2-dimethylpropanoic acid, and the second acid (ii) is pentanoic acid. Both are carboxylic acids, but the strength of an acid is influenced by the stability of its conjugate base.
Step 2: Consider the inductive effect in pair A. The bulky methyl groups in acid (i) are electron-donating, which destabilizes the conjugate base and makes the acid weaker. In contrast, acid (ii) has no such electron-donating groups, making its conjugate base more stable and the acid stronger.
Step 3: Analyze the acids in pair B. The first acid (i) is benzoic acid, and the second acid (ii) is 4-bromobenzoic acid. Both are aromatic carboxylic acids, but substituents on the benzene ring can influence acidity through inductive and resonance effects.
Step 4: Consider the substituent effects in pair B. Bromine in acid (ii) is an electron-withdrawing group due to its inductive effect, which stabilizes the conjugate base and increases the acidity. In contrast, the hydrogen substituent in acid (i) has no electron-withdrawing effect, making it less acidic.
Step 5: Conclude that in pair A, pentanoic acid (ii) is stronger due to the absence of destabilizing electron-donating groups, and in pair B, 4-bromobenzoic acid (ii) is stronger due to the electron-withdrawing effect of bromine.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acid Strength and Stability of Conjugate Base
The strength of an acid is often determined by the stability of its conjugate base. A more stable conjugate base corresponds to a stronger acid. Factors influencing stability include electronegativity, resonance, and inductive effects. For example, if a conjugate base can delocalize negative charge through resonance, it will be more stable, thus indicating a stronger acid.
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Stability of Conjugated Intermediates
Inductive Effect
The inductive effect refers to the electron-withdrawing or electron-donating effects of substituents on a molecule. Electron-withdrawing groups (like halogens) can stabilize the negative charge on a conjugate base, enhancing acid strength. In the given pairs, the presence of bromine in one of the acids can increase acidity due to its inductive effect, making the acid stronger.
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01:47Understanding the Inductive Effect.
Resonance Stabilization
Resonance stabilization occurs when a molecule can be represented by multiple valid Lewis structures, allowing for the delocalization of electrons. In carboxylic acids, resonance can stabilize the conjugate base formed after deprotonation. The more resonance structures available for the conjugate base, the more stable it is, leading to a stronger acid. This concept is crucial for comparing the acids in the provided pairs.
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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?
c.
d.
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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
What is the major product of each of the following reactions, assuming that one equivalent of each reagent is used in each reaction?
b.
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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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