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Why is the charge localised here: Image

It has negative charge in conjugation π-bond. So, why resonance is not possible?

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  • $\begingroup$ Welcome to Chemistry.SE! Take the tour to get familiar with this site. Mathematical expressions and equations can be formatted using $\LaTeX$ syntax. Please upload the image using the provided dialogue in the edit window. It would also help to see it in context. I can only assume the ion was formed from deprotonation of benzene, hence the lone pair will be orthogonal to the pi-system. $\endgroup$ – Martin - マーチン Nov 30 '17 at 6:05
  • $\begingroup$ Actually, I was trying to upload the image but each time it was unsuccessful. $\endgroup$ – DJ Koustav Nov 30 '17 at 6:48
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    $\begingroup$ chemistry.stackexchange.com/questions/50266/… $\endgroup$ – Mithoron Nov 30 '17 at 15:16
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If resonance was possible, once carbon would have 2 pi bonds and 2 sigma bonds, which means that particular carbon would be sp hybrid. It's orbitals would require 180 angle which is not possible for benzene ring to provide(only 120 is possible because it's a hexagon and all) And this negative charge with have a significant repulsion from the conjugated electrons. So this negative charge, it's existence itself is really unstable.

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    $\begingroup$ That is wrong. Very wrong. The molecule is not nearly as rigid as you propose it to be. And it is equally not as unstable as you make it to be. $\endgroup$ – Martin - マーチン Nov 30 '17 at 17:43
  • $\begingroup$ Provide me some data, saying that it's very wrong is just too vague. It is rigid because the system is planar and it's planarity is the reason for its stability. And you might be talking about some very very specific conditions under which it's stable. But in general case this won't even form. If you think of benzyne it's a partial overlap of p orbitals. That is different because that bond itself is incomplete overlap without harming the consistency of the structure. So before yelling 'wrong very wrong' enlighten me. $\endgroup$ – user55707 Nov 30 '17 at 17:47
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    $\begingroup$ The molecule is isoelectronic to pyridine. And I am most certainly not talking about benzyne. There are plenty of sources, including this site, at your disposal. I'm sure I do not need to educate you in the comment section. With wrong, however, I refer to your generally much too simplistic approach to this kind of problem. $\endgroup$ – Martin - マーチン Nov 30 '17 at 17:57
  • $\begingroup$ The word isoelectronic doesn't mean that it behaves the same way, or in no way have similar stability. The difference in electronegativity of carbon and nitrogen is a major factor why carbanions are not stable. And when you talk about pyridine, those electrons are not delocalised. In some examples carbanions are stable, but only in specific cases and special conditions. Changing one atom in a structure makes it's properties to change drastically. So isoelectronic molecules and similar molecules are useful to group certain molecules but when it's about stability, I don't see any correlation. $\endgroup$ – user55707 Nov 30 '17 at 18:03

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