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 71c

Chapter 9, Problem 71c

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

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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 (structures where all atoms satisfy the octet rule are more stable), formal charges (structures with fewer formal charges or charges on more electronegative atoms are more stable), and charge separation (structures with minimal charge separation are preferred).

Compare the resonance contributors based on their stability. The more stable resonance contributor will make a greater contribution to the resonance hybrid because it represents a lower-energy state.

Consider any additional factors, such as aromaticity (if applicable). Aromatic structures are particularly stable and will contribute more to the resonance hybrid. Similarly, avoid structures with highly unstable features, such as positive charges on electronegative atoms like oxygen or nitrogen.

Conclude which resonance contributor in the pair makes the greater contribution to the resonance hybrid based on the analysis of stability and other factors.

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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 structure of the molecule is a resonance hybrid, a weighted average of all valid resonance forms.

Resonance Hybrid

The resonance hybrid is the actual structure of a molecule that is formed from the combination of its resonance contributors. It represents a more stable configuration than any individual resonance structure due to the delocalization of electrons. The contribution of each resonance structure to the hybrid depends on factors such as formal charge, electronegativity, and overall stability.

Factors Affecting Resonance Contribution

The contribution of a resonance structure to the resonance hybrid is influenced by several factors, 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. Understanding these factors is essential for predicting the behavior of molecules in chemical reactions.

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