Textbook Question
Use resonance structures to identify the areas of high and low electron density in the following compounds:
i.
j.
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1. A Review of General Chemistry
Resonance Structures
6:19 minutesProblem 68(10)
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?
10. 
Verified step by step guidance1
Step 1: Identify the resonance contributors for the given species. Resonance contributors are alternative Lewis structures that differ only in the placement of electrons, not the arrangement of atoms.
Step 2: For the first species (image 1), focus on the carbonyl group (C=O) and the aromatic ring. The resonance contributors will involve the delocalization of electrons from the aromatic ring to the carbonyl group. Draw structures where the π-electrons from the aromatic ring interact with the carbonyl group.
Step 3: For the second species (image 2), examine the central carbon atom with a lone pair. Resonance contributors will involve the movement of electrons between the lone pair on the central carbon and the adjacent carbonyl groups. Draw structures where the lone pair forms a π-bond with one of the carbonyl groups, while the other carbonyl group accepts electrons.
Step 4: Evaluate the stability of each resonance contributor. Major contributors are those with full octets on all atoms, minimal formal charges, and charge separation that aligns with electronegativity trends. Minor contributors may have incomplete octets or unfavorable charge separation.
Step 5: Determine if any of the species have resonance contributors that contribute equally to the resonance hybrid. This occurs when all resonance structures have similar stability and energy levels, which is rare but possible in symmetric molecules or systems.
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Video duration:
6mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Resonance Structures
Resonance structures are different ways of drawing a molecule that represent the same arrangement of atoms but differ in the distribution of electrons. These structures help illustrate the delocalization of electrons within a molecule, which can stabilize it. The actual structure of the molecule is a resonance hybrid, a weighted average of all valid resonance forms, where more stable contributors have a greater influence.
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Major and Minor Contributors
In resonance theory, major contributors are resonance structures that are more stable and thus have a greater impact on the resonance hybrid. Factors influencing stability include the octet rule, charge distribution, and the presence of electronegative atoms. Minor contributors, while still valid, are less stable and contribute less to the overall resonance hybrid, often due to unfavorable charge placements or steric strain.
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Equal Contribution of Resonance Contributors
Some resonance contributors can contribute equally to the resonance hybrid if they are all equally stable and satisfy the same structural criteria. This typically occurs when the resonance forms have similar energy levels and do not violate the octet rule. Identifying such contributors is crucial for understanding the overall stability and reactivity of the molecule in question.
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