How does charge delocalization affect phenoxide anion stability?

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Discussion Overview

The discussion centers on the stability of the phenoxide anion and the role of charge delocalization over the ortho, para, and meta positions of aromatic rings. Participants explore theoretical explanations, resonance structures, and analogies to physical concepts.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions why delocalization of the negative charge increases the stability of the phenoxide anion, specifically noting the significance of ortho and para positions compared to the meta position.
  • Another participant suggests drawing resonance forms of the phenoxide ion to illustrate the charge distribution.
  • A participant explains that the ortho and para positions allow for better resonance and charge spreading, while the meta position does not facilitate this delocalization.
  • One participant challenges the explanation of stability based solely on delocalization, proposing an analogy to the "particle in a box" concept to discuss energy and charge delocalization further.
  • A later reply emphasizes that an increase in feasible resonance structures correlates with greater stability of the molecule.

Areas of Agreement / Disagreement

Participants express varying viewpoints on the mechanisms behind the stability of the phenoxide anion, with no consensus reached on the sufficiency of delocalization as an explanation.

Contextual Notes

Some assumptions regarding the relationship between resonance structures and stability are not fully explored, and the discussion includes references to physical analogies that may not directly apply to the chemical context.

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Why does delocalization of the negative charge over the ortho and para positions of aromatic rings increase the stability of the phenoxide anion? Why do the ortho and para positions increase the stability but not the meta position? Please explain. Thank you.
 
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Can you draw resonance forms of the phenoxide ion?
 
You see, the ortho and para forms allow the resonance to "spread out" the charge to the O- ion at the end, while the meta position is placed just so that it cannot achieve this.
 
Of course noting that the negative charge is more delocalized doesn't really explain why it is more stable!

Read about the "particle in a box" for an explanation. Consider a particle like an electron confined in a region of dimension L. The energy of that electron is expressed as a function of dimension L, or length, that the particle can move. If the electron is allowed to move more freely (L increases), it has a lower energy since http://en.wikipedia.org/wiki/Particle_in_a_box#cite_note-Davies5-3" The particle in a box is a one dimensional treatment but this is used as an approximation of the delocation length of an individual electron.
 
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http://chemistry.boisestate.edu/people/richardbanks/organic/phenol.gif

Google is just lovely at times.

In general, the as the number of feasible resonance structures increases, the more stable the molecule is, for the reasons chemisttree stated.
 
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Nice, clustro.
 

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