Textbook Question
Peroxyacetic acid (pKa = 8.2) is a much weaker acid than acetic acid (pKa = 4.74). Explain why peroxyacetic acid is a weaker acid than acetic acid.
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Ch. 2 - Acids and Bases; Functional Groups
Wade9th EditionOrganic ChemistryISBN: 9780135213728
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Table of contents
- Ch.1 - Structure and Bonding107
- Ch. 2 - Acids and Bases; Functional Groups115
- Ch.3 - Structure and Stereochemistry of Alkanes100
- Ch.4 - The Study of Chemical Reactions99
- Ch.5 - Stereochemistry93
- Ch.6 - Alkyl Halides; Nucleophilic Substitution118
- Ch. 7 - Structure and Synthesis of Alkenes; Elimination158
- Ch.8 - Reactions of Alkenes171
- Ch.9 - Alkynes91
- Ch.10 - Structure and Synthesis of Alcohols143
- Ch.11 - Reactions of Alcohols104
- Ch. 12 - Infrared Spectroscopy and Mass Spectrometry22
- Ch. 13 - Nuclear Magnetic Resonance Spectroscopy45
- Ch. 14 - Ethers, Epoxides, and Thioethers72
- Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy89
- Ch. 16 - Aromatic Compounds74
- Ch. 17 - Reactions of Aromatic Compounds126
- Ch. 18 - Ketones and Aldehydes193
- Ch. 19 - Amines129
- Ch. 20 - Carboxylic Acids77
- Ch. 21 - Carboxylic Acid Derivatives141
- Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds175
- Ch. 23 - Carbohydrates and Nucleic Acids93
- Ch. 24 - Amino Acids, Peptides, and Proteins54
Chapter 2, Problem 41b,c,d
The following compounds are listed in increasing order of acidity. In each case, the most acidic proton is shown in red.
b. Explain why X is a stronger acid than W.
c. Explain why Y is a stronger acid than X.
d. Explain why Z is a stronger acid than Y.
Verified step by step guidance1
Identify the structural differences between compounds W and X. Compound W has a methylene group (CH2) adjacent to the carbonyl, while compound X has an amide group (NH).
Consider the effect of the amide group in X. The nitrogen in the amide can participate in resonance with the carbonyl group, stabilizing the conjugate base more effectively than the methylene group in W.
Examine the structural difference between compounds X and Y. Compound Y has an additional hydroxyl group (OH) attached to the nitrogen, forming a hydroxamic acid.
Analyze the effect of the hydroxyl group in Y. The presence of the OH group increases the acidity by allowing additional resonance stabilization of the conjugate base, as well as potential hydrogen bonding interactions.
Compare compounds Y and Z. Compound Z is a carboxylic acid, which is generally more acidic due to the high resonance stabilization of its conjugate base (carboxylate ion) and the electronegative oxygen atoms that stabilize the negative charge.
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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 in organic chemistry is often measured using the pKa value, which indicates the strength of an acid. A lower pKa value corresponds to a stronger acid, meaning it more readily donates protons (H+). Understanding the relationship between pKa and acidity is crucial for comparing the acidity of different compounds.
Recommended video:
07:45
Identifying pKa values
Resonance Stabilization
Resonance stabilization occurs when a molecule can distribute its electron density across multiple structures, leading to increased stability. In the context of acidity, if the conjugate base formed after deprotonation can be stabilized by resonance, the original acid will be stronger. This concept helps explain why certain compounds have lower pKa values.
Recommended video:
03:43The radical stability trend.
Inductive Effect
The inductive effect refers to the electron-withdrawing or electron-donating effects of substituents on a molecule. Electronegative atoms or groups can stabilize the negative charge on a conjugate base through inductive withdrawal, enhancing acidity. This effect is important in comparing the acidity of compounds with different substituents.
Recommended video:
01:47Understanding the Inductive Effect.
Related Practice
Textbook Question
The following compound can become protonated on any of the three nitrogen atoms. One of these nitrogens is much more basic than the others, however.
b. Determine which nitrogen atom is the most basic.
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2
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Textbook Question
The Ka of phenylacetic acid is 5.2 × 10−5, and the pKa of propionic acid is 4.87.
c. Predict whether the following equilibrium will favor the reactants or the products.
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Textbook Question
Predict the products of the following acid–base reactions.
(a) H2SO4 + CH3COO– ⇌
(b) CH3COOH + (CH3)3N: ⇌
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Textbook Question
Hydrogen peroxide (HOOH) has a pKa of 11.6, making it roughly 10,000 times as strong an acid as water (pKa = 15.7). Explain why H2O2 is a stronger acid than H2O.
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Textbook Question
The following compound can become protonated on any of the three nitrogen atoms. One of these nitrogens is much more basic than the others, however.
a. Draw the important resonance forms of the products of protonation on each of the three nitrogen atoms.
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