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: 9780135213711당신이 사용하는 게 아니라요?교과서 변경

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

문제 68(5)

8장, 문제 68(5)

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?
5.

검증된 단계별 안내

Step 1: Analyze the given structure. The species shown is a nitro compound with a negatively charged oxygen atom, a positively charged nitrogen atom, and a carbon atom bonded to two methyl groups. The nitrogen atom is double-bonded to one oxygen atom and single-bonded to another oxygen atom with a negative charge.

Step 2: Identify possible resonance contributors. Resonance contributors involve the delocalization of electrons. In this case, the negative charge on the single-bonded oxygen can move to form a double bond with the nitrogen, while the double bond between nitrogen and the other oxygen can shift to place a negative charge on that oxygen.

Step 3: Draw the resonance structures. The first resonance structure will have the negative charge on the oxygen that was initially double-bonded to nitrogen, while the nitrogen will now be single-bonded to that oxygen and double-bonded to the other oxygen. The second resonance structure will restore the original positions of the charges and bonds.

Step 4: Evaluate the stability of the resonance contributors. The resonance structure where the negative charge is on the oxygen atom is more stable because oxygen is more electronegative and can better accommodate the negative charge. Both resonance structures contribute significantly to the resonance hybrid, but the one with the negative charge on oxygen is slightly more stable.

Step 5: Address part b of the question. In this case, the resonance contributors do not contribute equally to the resonance hybrid because one structure is slightly more stable due to the placement of the negative charge on the more electronegative oxygen atom.

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주요 개념

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Resonance Structures

Resonance structures are different Lewis structures for the same molecule that depict the same arrangement of atoms but differ in the distribution 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 forms, where more stable forms contribute more to the hybrid.

Major and Minor Contributors

In resonance theory, major contributors are resonance structures that are more stable and thus have a greater influence on the resonance hybrid. Factors that enhance stability include having a full octet, minimal formal charges, and the presence of electronegative atoms in appropriate positions. Minor contributors, on the other hand, are less stable and contribute less to the overall resonance hybrid due to factors like high formal charges or unfavorable electron arrangements.

Equal Contribution of Resonance Contributors

Some molecules may have resonance contributors that are equivalent in terms of stability and energy, leading to equal contribution to the resonance hybrid. This occurs when all resonance structures have similar formal charges, octet fulfillment, and overall stability. Identifying such cases is crucial for understanding the electronic structure of the molecule, as it indicates a high degree of delocalization and stability.