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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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 60c
Explain why N,N,2,6-tetramethylaniline (shown) is a much stronger base than N,N-dimethylaniline.
Verified step by step guidance1
Step 1: Begin by analyzing the structures of N,N,2,6-tetramethylaniline and N,N-dimethylaniline. Both molecules contain a nitrogen atom bonded to two methyl groups, but N,N,2,6-tetramethylaniline has additional methyl groups at the ortho positions (2 and 6) of the benzene ring.
Step 2: Understand the concept of basicity in amines. The basicity of an amine is determined by the availability of the lone pair of electrons on the nitrogen atom to accept a proton (H⁺). Factors that influence this availability include steric hindrance and electronic effects.
Step 3: Examine the steric effects in N,N,2,6-tetramethylaniline. The methyl groups at the ortho positions create steric hindrance, which prevents the nitrogen's lone pair from interacting effectively with the π-electrons of the benzene ring. This steric hindrance reduces conjugation between the nitrogen and the benzene ring, making the lone pair more available for protonation.
Step 4: Compare this to N,N-dimethylaniline. In this molecule, there are no ortho substituents, so the nitrogen's lone pair can delocalize into the benzene ring through resonance. This delocalization reduces the availability of the lone pair for protonation, making N,N-dimethylaniline a weaker base.
Step 5: Conclude that the steric hindrance caused by the ortho methyl groups in N,N,2,6-tetramethylaniline prevents resonance delocalization of the nitrogen's lone pair, increasing its basicity compared to N,N-dimethylaniline.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Basicity in Organic Chemistry
Basicity refers to the ability of a compound to accept protons (H+ ions). In organic chemistry, the strength of a base is influenced by the availability of its lone pair of electrons to bond with protons. Stronger bases have more available electron density, which allows them to more readily accept protons.
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What is an organic molecule?
Steric Hindrance
Steric hindrance occurs when the spatial arrangement of atoms in a molecule prevents certain interactions, such as protonation. In the case of N,N,2,6-tetramethylaniline, the presence of bulky methyl groups at the 2 and 6 positions creates a more favorable environment for the nitrogen's lone pair to interact with protons, enhancing its basicity compared to N,N-dimethylaniline, which has less steric bulk.
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02:53Understanding steric effects.
Electron-Donating Groups
Electron-donating groups, such as alkyl groups, increase the electron density on the nitrogen atom in amines, enhancing their basicity. In N,N,2,6-tetramethylaniline, the four methyl groups significantly increase the electron density on the nitrogen, making it a stronger base than N,N-dimethylaniline, which has only two methyl groups contributing to electron donation.
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Related Practice
Textbook Question
Basicity depends on availability of an electron pair to bond a proton. Correlate structural effects in these amines with their basicities.
(b) Explain:
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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
The following spectra for A and B correspond to two structural isomers. The NMR singlet at δ1.16 in spectrum A disappears when the sample is shaken with D2O. The singlet at δ0.6 ppm in the spectrum of B disappears on shaking with D2O. Propose structures for these isomers, and show how your structures correspond to the spectra. Show what cleavage is responsible for the base peak at m/z 44 in the mass spectrum of A and the prominent peak at m/z 58 in the mass spectrum of B.
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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
Guanidine (shown) is about as strong a base as hydroxide ion. Explain why guanidine is a much stronger base than most other amines.
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