Textbook Question
Explain why each compound is aromatic, antiaromatic, or nonaromatic.
(d)
(e)
(f)
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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 16c
Draw resonance forms to show the charge distribution on the pyrrole structure.
Verified step by step guidance1
Step 1: Recognize the pyrrole structure. Pyrrole is a five-membered aromatic ring containing one nitrogen atom. The nitrogen has a lone pair of electrons, and the ring is conjugated with alternating double bonds.
Step 2: Understand resonance in aromatic systems. Resonance occurs when electrons can delocalize across the conjugated system, stabilizing the molecule. In pyrrole, the lone pair on nitrogen can participate in resonance with the π-electrons of the ring.
Step 3: Draw the first resonance form. In this form, the lone pair on nitrogen moves to form a double bond between nitrogen and one of the adjacent carbon atoms. This causes the double bond in the ring to shift, creating a new resonance structure.
Step 4: Draw the second resonance form. In this form, the double bond from the previous step shifts further around the ring, and the negative charge appears on a different carbon atom. This continues the delocalization of electrons.
Step 5: Draw the third resonance form. The double bond shifts again, placing the negative charge on yet another carbon atom. This completes the set of resonance structures for pyrrole, showing how the charge is distributed across the ring.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Resonance Structures
Resonance structures are different Lewis structures for the same molecule that illustrate the delocalization of electrons. In the case of pyrrole, resonance forms show how the nitrogen atom can share its lone pair with the π system of the ring, leading to multiple valid representations of the molecule's electron distribution.
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Drawing Resonance Structures
Aromaticity
Aromaticity refers to the enhanced stability of cyclic compounds with conjugated π electrons that follow Hückel's rule (4n + 2 π electrons). Pyrrole is aromatic due to its five-membered ring containing a nitrogen atom, which contributes to the π system, allowing for resonance stabilization and unique chemical properties.
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Charge Distribution
Charge distribution in a molecule refers to how electron density is spread across its atoms. In pyrrole, the resonance forms illustrate that the charge is not localized but rather delocalized over the ring, affecting its reactivity and interactions with other molecules, particularly in electrophilic aromatic substitution reactions.
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Related Practice
Textbook Question
When 3-chlorocyclopropene is treated with AgBF4, AgCl precipitates. The organic product can be obtained as a crystalline material, soluble in polar solvents such as nitromethane but insoluble in hexane. When the crystalline material is dissolved in nitromethane containing KCl, the original 3-chlorocyclopropene is regenerated. Determine the structure of the crystalline material, and write equations for its formation and its reaction with chloride ion.
Textbook Question
Explain why each compound is aromatic, antiaromatic, or nonaromatic.
(a)
(b)
(c)
Textbook Question
Show which of the nitrogen atoms in purine are basic, and which one is not basic. For the nonbasic nitrogen, explain why its nonbonding electrons are not easily available to become protonated.
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Textbook Question
a. Explain how pyrrole is isoelectronic with the cyclopentadienyl anion.
b. Specifically, what is the difference between the cyclopentadienyl anion and pyrrole?
Textbook Question
The polarization of a carbonyl group can be represented by a pair of resonance structures:
Cyclopropenone and cycloheptatrienone are more stable than anticipated. Cyclopentadienone, however, is relatively unstable and rapidly undergoes a Diels–Alder dimerization. Explain.
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