Textbook Question
For each of these ions, draw the important resonance forms and predict which resonance form is likely to be the major contributor.
(c)
1
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Ch.1 - Structure and Bonding
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 1, Problem 44a
For each of these ions, draw the important resonance forms and predict which resonance form is likely to be the major contributor.
(a) 
Verified step by step guidance1
Identify the structure of the ion: The given ion is a five-membered ring with an oxygen atom and a positively charged CH2 group. This is a furan ring with a methylene group attached, carrying a positive charge.
Determine the possible resonance forms: In this structure, the positive charge can be delocalized through the pi system of the ring. Consider moving the pi electrons from the double bond adjacent to the positively charged carbon to form a new double bond between the oxygen and the carbon.
Draw the first resonance form: Move the pi electrons from the C=C double bond adjacent to the CH2+ group towards the CH2+ group, forming a new double bond between the CH2 and the adjacent carbon, and leaving a positive charge on the carbon that was part of the original double bond.
Draw the second resonance form: Move the pi electrons from the C=O double bond towards the oxygen atom, forming a lone pair on the oxygen and a positive charge on the carbon that was part of the C=O bond.
Predict the major contributor: The major resonance form is typically the one with the least charge separation and the most stable arrangement of charges. In this case, the resonance form where the positive charge is on the carbon adjacent to the oxygen (due to the electronegativity of oxygen) is likely to be the major contributor.
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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 a molecule that depict the same arrangement of atoms but differ in the distribution of electrons. They are used to represent delocalized electrons within certain molecules where the bonding cannot be expressed by a single Lewis structure. The true structure is a hybrid of all possible resonance forms, contributing to the molecule's stability.
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Drawing Resonance Structures
Major and Minor Resonance Contributors
In resonance, not all structures contribute equally to the resonance hybrid. The major contributor is the resonance form with the lowest energy, typically having the most covalent bonds, the least charge separation, and negative charges on the most electronegative atoms. Minor contributors have higher energy due to less favorable charge distributions or incomplete octets.
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Stability of Carbocations
Carbocations are positively charged carbon atoms, and their stability is influenced by factors such as hyperconjugation, resonance, and the inductive effect. Resonance can stabilize a carbocation if the positive charge can be delocalized over multiple atoms. In the given structure, the positive charge on the CH2 group can be stabilized by resonance with the adjacent oxygen atom, which can donate electron density through its lone pairs.
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Related Practice
Textbook Question
Draw the important resonance forms to show the delocalization of charges in the following ions. In each case, indicate the major resonance form(s).
(j)
(k)
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Textbook Question
In the following sets of resonance forms, label the major and minor contributors and state which structures would be of equal energy. Add any missing important resonance forms.
(d)
(e)
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Textbook Question
For each pair of ions, determine which ion is more stable. Use resonance forms to explain your answers.
(e)
(f)
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Textbook Question
Determine whether the following pairs of structures are actually different compounds or simply resonance forms of the same compounds.
i.
j.
k.
l.
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Textbook Question
For each of these ions, draw the important resonance forms and predict which resonance form is likely to be the major contributor.
(b)
3
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