Textbook Question
Which ion in each of the following pairs is more stable?
b.
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Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
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Bruice 8th EditionCh. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of BenzeneProblem 69a
Bruice 8th EditionCh. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of BenzeneProblem 69aChapter 9, Problem 69a
Which ion in each of the following pairs is more stable?
a. 
Verified step by step guidance1
Analyze the structures provided: The left structure represents a cyclopropyl anion (negative charge), while the right structure represents a cyclopropyl cation (positive charge). Cyclopropane is a strained ring system due to its small bond angles, which deviate significantly from the ideal tetrahedral angle of 109.5°.
Consider the electronic effects: The cyclopropyl ring has significant angle strain and torsional strain. The negative charge in the cyclopropyl anion is localized on the carbon atom, which is destabilized due to the strain and lack of resonance stabilization. On the other hand, the cyclopropyl cation benefits from hyperconjugation and inductive effects, which can help delocalize the positive charge to some extent.
Evaluate resonance and stabilization: The cyclopropyl cation is stabilized by the overlap of the σ-bonds in the ring with the empty p-orbital of the positively charged carbon atom. This interaction is known as σ-conjugation, which provides additional stability to the cation. The cyclopropyl anion lacks such stabilization mechanisms.
Compare the stability of the ions: The cyclopropyl cation is more stable than the cyclopropyl anion due to the presence of σ-conjugation and the ability to delocalize the positive charge, whereas the cyclopropyl anion suffers from localized negative charge and ring strain.
Conclude the comparison: Based on the above analysis, the cyclopropyl cation is the more stable ion in this pair.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Aromatic Stability
Aromatic compounds are particularly stable due to their cyclic structure and the delocalization of π electrons across the ring. This delocalization leads to a lower energy state, making aromatic systems more stable than non-aromatic or anti-aromatic compounds. The concept of aromaticity is governed by Hückel's rule, which states that a compound must have 4n + 2 π electrons to be considered aromatic.
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Resonance
Resonance refers to the phenomenon where a molecule can be represented by two or more valid Lewis structures, known as resonance structures. These structures contribute to the overall stability of the molecule, as the actual structure is a hybrid of these forms. In the context of the question, resonance can help explain the stability of the ions by showing how charge distribution can be stabilized through delocalization.
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03:04Drawing Resonance Structures
Charge Distribution
Charge distribution is crucial in determining the stability of ions. Ions with charges that can be delocalized over multiple atoms tend to be more stable than those with localized charges. In the given structures, analyzing how the positive charge is distributed can provide insights into which ion is more stable, as a more favorable charge distribution often leads to lower energy and increased stability.
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01:34Calculating formal and net charge.
Related Practice
Textbook Question
a. Draw resonance contributors for the following species. Do not include structures that are so unstable that their contributions to the resonance hybrid would be negligible. Indicate which are major contributors and which are minor contributors to the resonance hybrid.
b. Do any of the species have resonance contributors that all contribute equally to the resonance hybrid?
- CH3CH=CHOCH3
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Textbook Question
Which ion in each of the following pairs is more stable?
c.
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Textbook Question
Which ion in each of the following pairs is more stable?
d.
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Textbook Question
Which compound would you expect to have the greater heat of hydrogenation: 1,2-pentadiene or 1,4-pentadiene?
Textbook Question
a. Draw resonance contributors for the following species. Do not include structures that are so unstable that their contributions to the resonance hybrid would be negligible. Indicate which are major contributors and which are minor contributors to the resonance hybrid.
b. Do any of the species have resonance contributors that all contribute equally to the resonance hybrid?
8.
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