Textbook Question
What products are obtained when the following tertiary amines react with hydrogen peroxide followed by heat?
c.
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Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds
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. 19 - More About Amines • Reactions of Heterocyclic CompoundsProblem 33a
Bruice 8th EditionCh. 19 - More About Amines • Reactions of Heterocyclic CompoundsProblem 33aChapter 20, Problem 33a
a. Draw resonance contributors to show why pyridine-N-oxide is more reactive than pyridine toward electrophilic aromatic substitution.
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Identify the structure of pyridine-N-oxide. Pyridine-N-oxide is a pyridine ring with an oxygen atom bonded to the nitrogen via a coordinate covalent bond, giving the nitrogen a positive formal charge and the oxygen a negative formal charge.
Recall the concept of resonance. Resonance contributors are alternative Lewis structures that show the delocalization of electrons within a molecule. For pyridine-N-oxide, the negative charge on the oxygen can delocalize into the aromatic ring, enhancing electron density at certain positions.
Draw the resonance contributors for pyridine-N-oxide. Start by moving a lone pair of electrons from the negatively charged oxygen into the N-O bond, which pushes the π-electrons in the ring to different positions. This creates resonance structures where the negative charge is delocalized onto the carbon atoms in the ring.
Compare the resonance contributors of pyridine-N-oxide to those of pyridine. In pyridine, the nitrogen atom does not have a formal positive charge, and the electron density in the ring is lower. In contrast, the resonance contributors of pyridine-N-oxide show increased electron density at specific positions in the ring, making it more reactive toward electrophilic aromatic substitution.
Conclude that the increased electron density in pyridine-N-oxide, as shown by its resonance contributors, makes it more nucleophilic and thus more reactive toward electrophilic aromatic substitution compared to pyridine.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Resonance Structures
Resonance structures are different ways of drawing the same molecule that illustrate the delocalization of electrons. In the case of pyridine-N-oxide, resonance contributors can show how the presence of the N-oxide group affects electron density distribution, making certain positions on the aromatic ring more reactive toward electrophiles.
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Drawing Resonance Structures
Electrophilic Aromatic Substitution (EAS)
Electrophilic aromatic substitution is a fundamental reaction in organic chemistry where an electrophile replaces a hydrogen atom on an aromatic ring. The reactivity of the aromatic compound is influenced by the electron-donating or withdrawing effects of substituents, which can stabilize or destabilize the intermediate formed during the reaction.
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Electron-Withdrawing Groups
Electron-withdrawing groups (EWGs) are substituents that pull electron density away from the aromatic ring, often increasing the reactivity of the ring toward electrophiles. In pyridine-N-oxide, the oxygen atom of the N-oxide group acts as an EWG, enhancing the electrophilic attack at the ortho and para positions compared to unsubstituted pyridine.
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Related Practice
Textbook Question
The chemical shifts of the C-2 hydrogen in the spectra of pyrrole, pyridine, and pyrrolidine are 2.82 ppm, 6.42 ppm, and 8.50 ppm. Match each heterocycle with its chemical shift.
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Textbook Question
What products are obtained when the following tertiary amines react with hydrogen peroxide followed by heat?
d.
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Textbook Question
b. At what position does pyridine-N-oxide undergo electrophilic aromatic substitution?
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Textbook Question
Explain why pyrrole (pKa ~ 17) is a much stronger acid than ammonia (pKa = 36).
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Textbook Question
What products are obtained when the following tertiary amines react with hydrogen peroxide followed by heat?
a.
b.
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