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(3)

Chapter 9, Problem 68(3)

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?
3.

Verified step by step guidance

Step 1: Begin by identifying the species in question and determine if it has delocalized electrons, such as π-electrons or lone pairs, that can participate in resonance. Resonance contributors are alternative Lewis structures that differ only in the placement of electrons, not the arrangement of atoms.

Step 2: Draw the resonance contributors by moving electrons (π-electrons or lone pairs) while ensuring that the octet rule is satisfied for second-row elements like carbon, nitrogen, and oxygen. Use curved arrows to show the movement of electrons between resonance structures.

Step 3: Evaluate the stability of each resonance contributor. Major contributors are typically those with full octets, minimal formal charges, and charges placed on atoms with appropriate electronegativity. Minor contributors may have incomplete octets, higher formal charges, or charges on less electronegative atoms.

Step 4: Indicate which resonance contributors are major and which are minor. Major contributors will have a greater impact on the resonance hybrid, while minor contributors will have a smaller impact.

Step 5: For part b, analyze whether all resonance contributors are equally stable. If all contributors have similar stability (e.g., all have full octets and minimal formal charges), they will contribute equally to the resonance hybrid. Otherwise, contributors with greater stability will dominate.

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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 violate the octet rule, making them less stable and thus contributing less to the overall hybrid.

Equal Contribution of Resonance Contributors

Some species may have resonance contributors that contribute equally to the resonance hybrid. This occurs when all structures are of similar stability and have comparable energy levels. In such cases, the resonance hybrid reflects an average of these structures, leading to a more stable overall molecule, as the electron density is evenly distributed among the contributing forms.

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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.