Textbook Question
Give an example for each of the following:
c. a β-keto aldehyde
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Ch. 17 - Reactions at the Alpha-Carbon
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
Chapter 18, Problem 4
Explain why the -hydrogen of an N,N-disubstituted amide is less acidic (pKa = 30) than the -hydrogen of an ester (pKa = 25).
Verified step by step guidance1
Identify the functional groups in the molecules: An N,N-disubstituted amide contains a carbonyl group (C=O) attached to a nitrogen atom with two substituents, while an ester contains a carbonyl group attached to an oxygen atom bonded to an alkyl group.
Recognize the key difference in electronegativity: The nitrogen atom in the amide is less electronegative than the oxygen atom in the ester. This means the nitrogen in the amide donates electron density more effectively to the carbonyl group, reducing the overall electron-withdrawing effect of the carbonyl group.
Understand the impact on the α-hydrogen: The α-hydrogen (the hydrogen on the carbon adjacent to the carbonyl group) is more acidic when the carbonyl group strongly withdraws electron density. In the ester, the oxygen atom enhances the electron-withdrawing effect of the carbonyl group, making the α-hydrogen more acidic. In contrast, the nitrogen in the amide reduces the electron-withdrawing effect, making the α-hydrogen less acidic.
Consider resonance stabilization of the conjugate base: When the α-hydrogen is removed, the resulting carbanion (conjugate base) can be stabilized by resonance with the carbonyl group. In the ester, the oxygen atom's higher electronegativity allows for better resonance stabilization of the conjugate base compared to the amide, where the nitrogen's electron-donating nature reduces resonance stabilization.
Conclude the reasoning: The combination of reduced electron-withdrawing ability and less effective resonance stabilization in the amide compared to the ester explains why the α-hydrogen of an N,N-disubstituted amide is less acidic (higher pKa) than the α-hydrogen of an ester.
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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 tendency of a compound to donate a proton (H+). The pKa value is a quantitative measure of this acidity; lower pKa values indicate stronger acids. In organic chemistry, the stability of the resulting conjugate base after deprotonation significantly influences acidity. Understanding pKa values helps compare the acidity of different functional groups.
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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. In the case of esters, the conjugate base formed after deprotonation can stabilize through resonance with the carbonyl group, enhancing its stability. This stabilization contributes to the higher acidity of esters compared to N,N-disubstituted amides.
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03:43The radical stability trend.
Inductive Effect
The inductive effect refers to the electron-withdrawing or electron-donating influence of substituents on a molecule. In N,N-disubstituted amides, the presence of electron-donating alkyl groups can reduce the acidity of the a-hydrogen by destabilizing the conjugate base. This contrasts with esters, where the carbonyl group can exert a stronger electron-withdrawing effect, enhancing acidity.
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01:47Understanding the Inductive Effect.
Related Practice
Textbook Question
Give an example for each of the following:
b. a β-diester
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Textbook Question
Rank the compounds in each of the following groups from strongest acid to weakest acid:
c.
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Textbook Question
Rank the compounds in each of the following groups from strongest acid to weakest acid:
a.
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Textbook Question
Explain why a base can remove a proton from the α-carbon of N,N-dimethylethanamide but not from the α-carbon of either N-methylethanamide or ethanamide.
Textbook Question
Explain why 92% of 2,4-pentanedione exists as the enol tautomer in hexane but only 15% of this compound exists as the enol tautomer in water.
3
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