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: 9780135213711Not the one you use?Change textbook

Bruice 8th Edition

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

Problem 68(6)

Chapter 9, Problem 68(6)

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?
6.

Verified step by step guidance

Identify the species in question and determine if it has delocalized electrons, such as lone pairs, π bonds, or charges, which can participate in resonance.

Draw all possible resonance contributors by moving electrons (lone pairs or π electrons) while ensuring that the octet rule is not violated for second-row elements and that formal charges are minimized.

Evaluate the stability of each resonance structure by considering factors such as the placement of charges (negative charges on more electronegative atoms, positive charges on less electronegative atoms) and the number of covalent bonds. Label the most stable structures as major contributors and less stable ones as minor contributors.

For part b, analyze the resonance contributors to determine if they are equivalent in terms of stability (e.g., identical structures with charges or bonds distributed symmetrically). If all contributors are equivalent, they contribute equally to the resonance hybrid.

Summarize your findings by indicating which contributors are major or minor and whether any species have resonance contributors that contribute equally to the resonance hybrid.

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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 depict the same arrangement of atoms but differ in the placement of electrons. These structures help illustrate the delocalization of electrons within a molecule, which contributes to its stability. The actual structure of the molecule is a resonance hybrid, a weighted average of all valid resonance contributors, where more stable structures contribute more to the hybrid.

Major and Minor Contributors

In resonance theory, major contributors are those resonance structures that are more stable and thus have a greater influence on the resonance hybrid. Factors that determine stability include the octet rule, charge distribution, and the presence of formal charges. Minor contributors, while still valid, are less stable and contribute less to the overall resonance hybrid, often due to unfavorable charge placements or incomplete octets.

Equally Contributing Resonance Structures

Some molecules may have resonance contributors that are equally stable, meaning they contribute equally to the resonance hybrid. This occurs when all structures satisfy the same stability criteria, such as having a full octet and minimal formal charges. Identifying such structures is crucial for understanding the overall electronic distribution in the molecule, as it indicates a high degree of resonance stabilization.

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Drawing Contributing Structures

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

b. Do any of the species have resonance contributors that all contribute equally to the resonance hybrid?

12.

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Textbook Question

b. Do any of the species have resonance contributors that all contribute equally to the resonance hybrid?

14.

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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?

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Textbook Question

b. Do any of the species have resonance contributors that all contribute equally to the resonance hybrid?

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Textbook Question

b. Do any of the species have resonance contributors that all contribute equally to the resonance hybrid?

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