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(12)

Chapter 9, Problem 68(12)

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?
12.

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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 (using curved arrows) while adhering to the rules of resonance: (1) Do not exceed the octet rule for second-row elements, (2) Maintain the same number of electrons, and (3) Only move π electrons or lone pairs, not σ bonds.

Evaluate the stability of each resonance structure based on factors such as: (1) Full octets on atoms, (2) Minimal formal charges, and (3) Negative charges on more electronegative atoms or positive charges on less electronegative atoms. Label the major contributors (most stable) and minor contributors (less stable).

For part b, analyze the resonance contributors to determine if they are all equivalent in terms of stability. If all contributors have the same formal charges, atom connectivity, and distribution of electrons, they contribute equally to the resonance hybrid.

Summarize your findings by indicating which resonance contributors are major or minor and whether any species have resonance contributors that contribute equally to the 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 delocalization of electrons. These structures help illustrate how electrons are distributed across the molecule, contributing to its overall stability. While individual resonance structures may not represent the actual molecule, the resonance hybrid, which is a weighted average of these structures, provides a more accurate depiction of electron distribution.

Major and Minor Contributors

In resonance theory, not all resonance structures contribute equally to the resonance hybrid. Major contributors are those that are more stable, typically having full octets, minimal formal charges, and favorable charge distribution. Minor contributors, on the other hand, may have higher energy due to factors like charge separation or incomplete octets, making their contribution to the hybrid less significant.

Equally Contributing Resonance Structures

Some molecules may have resonance contributors that contribute equally to the resonance hybrid, meaning they have similar stability and energy levels. This occurs when the structures have comparable formal charges and fulfill the octet rule similarly. Identifying such structures is crucial for understanding the overall electronic structure and reactivity of the molecule, as it indicates a high degree of resonance stabilization.

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Drawing Contributing Structures

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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.