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(9)

Chapter 9, Problem 68(9)

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?
9.

Verified step by step guidance

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

Draw the resonance contributors by moving electrons (using curved arrows) to show how the π electrons or lone pairs can be redistributed. Ensure that each structure follows the rules of valence and does not violate the octet rule (except for elements that can expand their octet, such as sulfur or phosphorus).

Evaluate the stability of each resonance contributor. Major contributors are typically those with a full octet on all atoms, minimal formal charges, and negative charges on more electronegative atoms. Minor contributors may have incomplete octets, more formal charges, or charges on less electronegative atoms.

Label each resonance contributor as either a major or minor contributor based on the stability analysis performed in the previous step.

For part b, analyze the resonance contributors to determine if they are all equivalent in terms of stability. If all contributors have the same structure and stability (e.g., equivalent formal charges and atom arrangements), then they contribute equally to the resonance hybrid. Otherwise, they contribute unequally.

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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.

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 distributions. Minor contributors, on the other hand, may have significant formal charges or incomplete octets, making them less stable and thus contributing less to the overall hybrid structure.

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 have similar energy levels and stability, often seen in symmetrical molecules. Identifying such contributors is crucial for understanding the overall electronic structure and reactivity of the species in question.

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Guided course

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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.