Textbook Question
Show how the substituents containing the azo group (N=N) can facilitate both electrophilic and nucleophilic aromatic substitution.
(a)
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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 61b
Basicity depends on availability of an electron pair to bond a proton. Correlate structural effects in these amines with their basicities.
(b) Explain:
Verified step by step guidance1
Step 1: Analyze the structures provided. Both molecules contain an amine group (-NH₂) and a nitro group (-NO₂) attached to aromatic rings. The first structure has a methyl group (-CH₃) attached to the ring containing the nitro group, while the second structure lacks this methyl group.
Step 2: Understand the concept of basicity. Basicity depends on the availability of the lone pair of electrons on the nitrogen atom in the amine group to bond with a proton (H⁺). Electron-donating groups increase basicity by making the lone pair more available, while electron-withdrawing groups decrease basicity by delocalizing or withdrawing electron density.
Step 3: Examine the effect of the nitro group (-NO₂). The nitro group is an electron-withdrawing group due to its strong electronegativity and resonance effects. It decreases the electron density on the amine nitrogen, reducing its basicity.
Step 4: Consider the role of the methyl group (-CH₃) in the first structure. The methyl group is an electron-donating group via hyperconjugation and inductive effects. It slightly counteracts the electron-withdrawing effect of the nitro group, making the amine nitrogen in the first structure more basic compared to the second structure.
Step 5: Conclude that the first structure, with the methyl group, is a stronger base than the second structure because the methyl group increases the availability of the lone pair on the amine nitrogen by donating electron density.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Basicity of Amines
Basicity in amines refers to their ability to accept protons (H+) due to the presence of a lone pair of electrons on the nitrogen atom. The strength of an amine as a base is influenced by the availability of this lone pair, which can be affected by the surrounding structural environment, such as electron-donating or withdrawing groups.
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07:12
Reductive Amination
Inductive Effect
The inductive effect describes how the presence of electronegative atoms or groups can withdraw electron density from adjacent atoms, affecting their reactivity. In amines, electron-withdrawing groups decrease basicity by stabilizing the lone pair on nitrogen, while electron-donating groups enhance basicity by increasing electron density around the nitrogen atom.
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01:47Understanding the Inductive Effect.
Steric Hindrance
Steric hindrance refers to the repulsion between bulky groups that can impede the approach of protons to the nitrogen atom in amines. Increased steric hindrance can reduce the basicity of an amine by making it more difficult for the nitrogen to interact with protons, thus affecting its ability to act as a base.
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02:53Understanding steric effects.
Related Practice
Textbook Question
Reductive amination of aldehydes and ketones is a versatile method for attaching alkyl groups to amines, but the alkyl group is restricted to a 1° or 2° carbon by this method. Prof. Phil Baran of Scripps Research Institute has reported (Science, 2015, 348 (6237), 886–891) a novel way to reduce an aromatic nitro group and add the resulting amine to an alkene so that the aromatic amine is bonded to a 3° carbon—all in a continuous sequence of reactions.
For example:
Predict the products using these starting materials, all of which are reported in this paper.
(c)
(d)
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Textbook Question
Basicity depends on availability of an electron pair to bond a proton. Correlate structural effects in these amines with their basicities.
(a) Explain this order:
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Textbook Question
Basicity depends on availability of an electron pair to bond a proton. Correlate structural effects in these amines with their basicities.
(c) The pKb of this compound is −2.3, making it not only a stronger base than a typical aniline, but even stronger than hydroxide ion. Explain its remarkable basicity.
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Textbook Question
Show why p-nitroaniline is a much weaker base (3 pKb units weaker) than aniline.
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Textbook Question
Explain why N,N,2,6-tetramethylaniline (shown) is a much stronger base than N,N-dimethylaniline.
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