Textbook Question
Propose a mechanism to show the individual alkylations that form this quaternary ammonium salt.
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Ch. 19 - Amines
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 19, Problem 14a
(a) Propose a mechanism for the reaction of 2-bromopyridine with sodium amide to give 2-aminopyridine.
Verified step by step guidance1
Identify the type of reaction: This is a nucleophilic substitution reaction where sodium amide (NaNH₂) acts as a strong nucleophile and base, replacing the bromine atom on 2-bromopyridine with an amino group (-NH₂).
Recognize the role of sodium amide: Sodium amide (NaNH₂) dissociates into Na⁺ and NH₂⁻. The NH₂⁻ ion is a strong nucleophile and will attack the electrophilic carbon atom bonded to the bromine in 2-bromopyridine.
Describe the first step of the mechanism: The NH₂⁻ ion attacks the carbon atom at the 2-position of the pyridine ring (where bromine is attached). This leads to the formation of a Meisenheimer complex (an intermediate where the aromaticity of the pyridine ring is temporarily lost).
Explain the elimination step: The bromide ion (Br⁻) is expelled from the intermediate, restoring the aromaticity of the pyridine ring. This results in the formation of 2-aminopyridine.
Summarize the overall reaction: The reaction proceeds via nucleophilic aromatic substitution (SNAr) mechanism, where the bromine atom is replaced by the amino group (-NH₂) to yield 2-aminopyridine as the final product.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Nucleophilic Substitution
Nucleophilic substitution is a fundamental reaction mechanism in organic chemistry where a nucleophile attacks an electrophile, resulting in the replacement of a leaving group. In the case of 2-bromopyridine, the bromine atom acts as a leaving group, while sodium amide provides the nucleophile, which is the amide ion (NH2-). Understanding this mechanism is crucial for predicting the outcome of the reaction.
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Nucleophiles and Electrophiles can react in Substitution Reactions.
Electrophilicity of Aromatic Compounds
Aromatic compounds, like pyridine, exhibit unique reactivity due to their stable ring structure and electron-rich nature. The nitrogen atom in pyridine is less nucleophilic than typical amines, but it can still participate in nucleophilic substitution reactions. Recognizing the electrophilic character of the bromine in 2-bromopyridine is essential for understanding how the nucleophile interacts with the aromatic system.
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Mechanism of Amine Formation
The formation of amines from halogenated compounds typically involves a two-step mechanism: nucleophilic attack followed by elimination of the leaving group. In this reaction, the amide ion attacks the carbon bonded to the bromine, forming a new C-N bond, and subsequently, the bromine is expelled. This process is vital for synthesizing amines, which are important functional groups in organic chemistry.
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Related Practice
Textbook Question
We have considered nucleophilic aromatic substitution of pyridine at the 2-position and 3-position but not at the 4-position. Complete the three possible cases by showing the mechanism for the reaction of methoxide ion with 4-chloropyridine. Show how the intermediate is stabilized by delocalization of the charge onto the nitrogen atom.
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Textbook Question
(b) When 3-bromopyridine is used in this reaction, stronger reaction conditions are required and a mixture of 3-aminopyridine and 4-aminopyridine results. Propose a mechanism to explain this curious result.
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Textbook Question
Propose a mechanism for nitration of pyridine at the 4-position, and show why this orientation is not observed.
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Textbook Question
Propose a mechanism for the sulfonation of pyridine, and point out why sulfonation occurs at the 3-position.
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Textbook Question
Show how you would use direct alkylation to synthesize the following compounds.
(a) benzyltrimethylammonium iodide
(b) pentan-1-amine
(c) benzylamine
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