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 33b
Bruice 8th EditionCh. 19 - More About Amines • Reactions of Heterocyclic CompoundsProblem 33bChapter 20, Problem 33b
b. At what position does pyridine-N-oxide undergo electrophilic aromatic substitution?
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Pyridine-N-oxide is a derivative of pyridine where an oxygen atom is bonded to the nitrogen atom, creating a positively charged nitrogen and a negatively charged oxygen. This alters the electronic distribution in the ring, making it different from regular pyridine.
In electrophilic aromatic substitution (EAS), the position of substitution is determined by the electronic effects of substituents. The oxygen in pyridine-N-oxide withdraws electron density from the nitrogen atom, which in turn affects the electron density at the various positions of the aromatic ring.
The resonance structures of pyridine-N-oxide show that the electron density is reduced at the ortho (positions 2 and 6) and para (position 4) positions relative to the nitrogen atom. However, the meta positions (positions 3 and 5) retain relatively higher electron density.
Since electrophiles are attracted to regions of higher electron density, the electrophilic aromatic substitution reaction will preferentially occur at the meta positions (positions 3 and 5) of pyridine-N-oxide.
To summarize, pyridine-N-oxide undergoes electrophilic aromatic substitution at the meta positions (positions 3 and 5) due to the electronic effects of the N-oxide group, which directs substitution to these positions.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
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. This process typically involves the formation of a sigma complex, where the aromaticity is temporarily lost, followed by deprotonation to restore aromaticity. Understanding EAS is crucial for predicting the reactivity of aromatic compounds, including heterocycles like pyridine.
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Pyridine and its Derivatives
Pyridine is a six-membered aromatic ring containing one nitrogen atom, which influences its reactivity compared to benzene. The nitrogen atom in pyridine is electron-withdrawing due to its electronegativity, which affects the positions where electrophilic substitution can occur. Recognizing the role of nitrogen in pyridine derivatives is essential for determining the regioselectivity of EAS reactions.
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Regioselectivity in Electrophilic Aromatic Substitution
Regioselectivity refers to the preference of an electrophile to attack specific positions on an aromatic ring during substitution reactions. In the case of pyridine-N-oxide, the presence of the nitrogen atom and the oxygen atom influences the electron density on the ring, making certain positions more favorable for electrophilic attack. Understanding regioselectivity helps predict the outcome of reactions involving substituted aromatic compounds.
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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
Propose a mechanism for the following reaction:
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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
a. Draw resonance contributors to show why pyridine-N-oxide is more reactive than pyridine toward electrophilic aromatic substitution.
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