Why does stabilization due to resonance increase polarity?
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an alternative browser.
You should upgrade or use an alternative browser.
Quick Chem Question
- Thread starter ajumobim
- Start date
- Joined
- Feb 3, 2015
- Messages
- 335
- Reaction score
- 152
In most cases, stabilization due to resonance should decrease polarity. Because instead of having a full charge at one point in space and thereby creating a strong dipole moment, you're distributing the charge over space so that you reduce the effective dipole moment of the molecule. Think of an allyl anion. If you didn't have resonance, you would have a really polar molecule because the charge is localized at one end of the molecule. If you have resonance, the charge can delocalize through the vacant p-orbitals donated from each carbon and be distributed between the two terminal carbons (can't be on the middle one because there is a node there).
In most cases, stabilization due to resonance should decrease polarity. Because instead of having a full charge at one point in space and thereby creating a strong dipole moment, you're distributing the charge over space so that you reduce the effective dipole moment of the molecule. Think of an allyl anion. If you didn't have resonance, you would have a really polar molecule because the charge is localized at one end of the molecule. If you have resonance, the charge can delocalize through the vacant p-orbitals donated from each carbon and be distributed between the two terminal carbons (can't be on the middle one because there is a node there).
This explanation makes sense, however in TBR an explanation for a question states "At physiological pH, arachidonic acid has its carboxyl hydrogen ionized. The two oxygen atoms on the carboxylic acid group will share the negative charge between them (through resonance). This leads to stabilization of that functional group and an increased polarity."
- Joined
- Feb 3, 2015
- Messages
- 335
- Reaction score
- 152
This explanation makes sense, however in TBR an explanation for a question states "At physiological pH, arachidonic acid has its carboxyl hydrogen ionized. The two oxygen atoms on the carboxylic acid group will share the negative charge between them (through resonance). This leads to stabilization of that functional group and an increased polarity."
Okay, well the stabilization part is correct. But I don't know what "polarity" the TBR explanation is referring to. I think in this context, they may be referring to polarity as a measure of how the charge is distributed - like polarization.
If this is referring to the question with arachiodonic acid, i believe the distinction is between polarity and stabilization. In this particular case with a carboxylic acid, there can be formal charges (polarity) in the molecule because the polar form is stabilized by resonance. So if the polarity is favorable (negative charges on electronegative atoms etc) then resonance promotes the polarity, i.e. we get the polarity through resonance. But as livelifetothefullest said, if we had unfavorable polarity, i.e. carbon carrying a negative charge, resonance can relieve that strain by distributing the electrons.
To use an example, forming an enolate via loss of H+ and a resulting carbanion is only favourable because of resonance, which stabilizes the negative charge and so promotes the polarity. I hope that makes sense, i am trying to get into the mind of whoever wrote that explanation!!
To use an example, forming an enolate via loss of H+ and a resulting carbanion is only favourable because of resonance, which stabilizes the negative charge and so promotes the polarity. I hope that makes sense, i am trying to get into the mind of whoever wrote that explanation!!
