Textbook Question
Propose a mechanism to show the individual alkylations that form this quaternary ammonium salt.
1
views
Ch. 19 - Amines
Wade9th EditionOrganic ChemistryISBN: 9780135213728
Not the one you use?Change textbookSelect a different textbook
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 14b
(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.
Verified step by step guidance1
Identify the reaction type: The problem involves the conversion of 3-bromopyridine to a mixture of 3-aminopyridine and 4-aminopyridine. This suggests a nucleophilic aromatic substitution (NAS) mechanism, which is common for halogenated aromatic compounds under strong conditions.
Analyze the structure of 3-bromopyridine: The bromine atom is attached to the 3-position of the pyridine ring. Pyridine is an electron-deficient aromatic ring due to the electronegativity of the nitrogen atom, which makes it susceptible to nucleophilic attack under appropriate conditions.
Propose the first step of the mechanism: Under strong reaction conditions, the nucleophile (likely an amine or ammonia) attacks the 3-position of the pyridine ring, displacing the bromine atom. This occurs via an addition-elimination mechanism, where the nucleophile adds to the ring, forming a Meisenheimer complex (an intermediate with a negatively charged aromatic ring).
Explain the formation of 4-aminopyridine: The strong reaction conditions can lead to rearrangement of the intermediate. The negative charge in the Meisenheimer complex can delocalize, allowing the nucleophile to migrate to the 4-position of the pyridine ring. This results in the formation of 4-aminopyridine as a side product.
Conclude with the product mixture: The reaction conditions favor both direct substitution at the 3-position and rearrangement to the 4-position, leading to a mixture of 3-aminopyridine and 4-aminopyridine. The ratio of these products depends on the reaction conditions, such as temperature, solvent, and nucleophile concentration.
Verified video answer for a similar problem:
This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
8mWas this helpful?
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 in organic chemistry where a nucleophile attacks an electrophile, replacing a leaving group. In the case of 3-bromopyridine, the bromine atom acts as a leaving group, and the reaction conditions influence the nucleophile's ability to attack the aromatic ring, leading to the formation of different products.
Recommended video:
Guided course
01:47
Nucleophiles and Electrophiles can react in Substitution Reactions.
Aromaticity and Electrophilic Substitution
Aromatic compounds, like pyridine, exhibit unique stability due to their delocalized π-electron systems. Electrophilic substitution reactions in aromatic systems can lead to regioselectivity, where the position of substitution is influenced by the electronic effects of substituents. In this case, the presence of the bromine atom affects the reactivity and orientation of the nucleophile.
Recommended video:
Guided course
03:07EAS Review
Regioselectivity
Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others when multiple possibilities exist. In the reaction involving 3-bromopyridine, the formation of both 3-aminopyridine and 4-aminopyridine suggests that the nucleophile can attack at different positions on the aromatic ring, influenced by steric and electronic factors, leading to a mixture of products.
Recommended video:
Guided course
05:09Heck Reaction
Related Practice
Textbook Question
(a) Propose a mechanism for the reaction of 2-bromopyridine with sodium amide to give 2-aminopyridine.
3
views
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.
1
views
Textbook Question
Propose a mechanism for the sulfonation of pyridine, and point out why sulfonation occurs at the 3-position.
2
views
Textbook Question
Give the products expected from the following reactions.
(a) acetyl chloride + ethylamine
(b)
(c)
7
views
Textbook Question
Show how you would use direct alkylation to synthesize the following compounds.
(a) benzyltrimethylammonium iodide
(b) pentan-1-amine
(c) benzylamine
2
views