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 71d

Chapter 9, Problem 71d

Which resonance contributor in each pair makes the greater contribution to the resonance hybrid?
d.

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Identify the resonance contributors in the given pair. Resonance contributors are different Lewis structures that represent the same molecule or ion, differing only in the placement of electrons (not atoms).

Evaluate the stability of each resonance contributor. Stability is influenced by factors such as the octet rule, formal charges, and electronegativity. For example, a structure where all atoms satisfy the octet rule is generally more stable.

Check the formal charges on each resonance contributor. Structures with fewer formal charges or charges that are minimized are more stable. Additionally, negative charges are more stable on more electronegative atoms, while positive charges are more stable on less electronegative atoms.

Consider charge separation. Resonance contributors with less charge separation (i.e., fewer positive and negative charges spread across the molecule) are generally more stable and contribute more to the resonance hybrid.

Determine which resonance contributor is more stable based on the above criteria. The more stable resonance contributor will make the greater contribution 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 is crucial for understanding its stability and reactivity. The actual molecule is a resonance hybrid, a weighted average of all valid resonance structures.

Resonance Hybrid

The resonance hybrid is the actual structure of a molecule that is represented as a combination of its resonance contributors. It reflects the delocalization of electrons across multiple bonds, leading to increased stability. The contribution of each resonance structure to the hybrid depends on factors like formal charge, electronegativity, and the overall stability of the structure.

Factors Affecting Resonance Contribution

Several factors determine the contribution of a resonance structure to the resonance hybrid, including the stability of the structure, the presence of formal charges, and the arrangement of electrons. Structures with minimal formal charges, full octets, and more electronegative atoms bearing negative charges are generally more stable and thus contribute more significantly to the resonance hybrid.

Which resonance contributor in each pair makes the greater contribution to the resonance hybrid? d.