Textbook Question
Each of the following heterocycles includes one or more nitrogen atoms. Classify each nitrogen atom as strongly basic or weakly basic, according to the availability of its lone pair of electrons.
(d)
(e)
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Ch. 16 - Aromatic Compounds
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 16, Problem 34a,b,c
Each of the following heterocycles includes one or more nitrogen atoms. Classify each nitrogen atom as strongly basic or weakly basic, according to the availability of its lone pair of electrons.
(a) 
(b) 
(c) 
Verified step by step guidance1
Step 1: Analyze the nitrogen atoms in structure (i). The molecule is a pyrimidine derivative. The nitrogen atom with the methyl group attached has its lone pair localized and not involved in resonance with the aromatic ring, making it strongly basic. The other nitrogen atom has its lone pair delocalized into the aromatic ring, making it weakly basic.
Step 2: Examine the nitrogen atom in structure (ii). This molecule is a morpholine derivative. The nitrogen atom has its lone pair localized and not involved in resonance or conjugation with the oxygen atom or the ring system, making it strongly basic.
Step 3: Evaluate the nitrogen atom in structure (iii). This molecule is an oxazole derivative. The nitrogen atom has its lone pair delocalized into the aromatic ring system, making it weakly basic.
Step 4: Consider the role of resonance and aromaticity in determining the basicity of nitrogen atoms. Lone pairs that are delocalized into aromatic systems are less available for protonation, reducing basicity. Lone pairs that are localized and not involved in resonance are more available for protonation, increasing basicity.
Step 5: Summarize the classifications: (i) one strongly basic nitrogen and one weakly basic nitrogen, (ii) strongly basic nitrogen, (iii) weakly basic nitrogen.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Basicity of Nitrogen
Basicity in organic chemistry refers to the ability of a compound to accept protons (H+). Nitrogen atoms can exhibit basicity due to the presence of a lone pair of electrons. The strength of basicity is influenced by the availability of this lone pair; if it is readily available for bonding with protons, the nitrogen is considered strongly basic.
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06:21
Understanding the difference between basicity and nucleophilicity.
Aromaticity and Electron Delocalization
Aromatic compounds are characterized by a cyclic structure with conjugated pi electrons that are delocalized across the ring. This delocalization can stabilize the molecule but also affects the availability of lone pairs on heteroatoms like nitrogen. In aromatic systems, lone pairs may participate in resonance, reducing their availability for protonation and thus weakening basicity.
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08:19Intro to Aromaticity
Inductive and Resonance Effects
Inductive effects arise from the electronegativity of atoms within a molecule, influencing the electron density around the nitrogen atom. Resonance effects occur when lone pairs can be delocalized into a pi system. Both effects can either enhance or diminish the basicity of nitrogen atoms, depending on their structural context within the heterocycle.
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01:47Understanding the Inductive Effect.
Related Practice
Textbook Question
The following molecules and ions are grouped by similar structures. Classify each as aromatic, antiaromatic, or nonaromatic. For the aromatic and antiaromatic species, give the number of pi electrons in the ring.
(c)
4
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Textbook Question
Some of the following compounds show aromatic properties, and others do not.
1. Predict which ones are likely to be aromatic, and explain why they are aromatic.
2. Predict which nitrogen atoms are more basic than water and which are less basic.
(d)
1
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Textbook Question
The following molecules and ions are grouped by similar structures. Classify each as aromatic, antiaromatic, or nonaromatic. For the aromatic and antiaromatic species, give the number of pi electrons in the ring.
(g)
1
views
Textbook Question
Some of the following compounds show aromatic properties, and others do not.
1. Predict which ones are likely to be aromatic, and explain why they are aromatic.
(a)
(b)
(c)
Textbook Question
The following molecules and ions are grouped by similar structures. Classify each as aromatic, antiaromatic, or nonaromatic. For the aromatic and antiaromatic species, give the number of pi electrons in the ring.
(d)