In inorganic chemistry, I learnt that stability of some atoms like ozone cannot be explained by one structure alone and hence the hybrid of possible structures is taken and assumed to be the structure and this is called resonance structure.

However, the book clearly states that it is wrong to assume that electrons move about back and forth alternating between the two structures, and that resonance is a theoretical concept only.

Here's an example for ozone. enter image description here

But in organic chemistry I learnt that resonance means electrons moving around and in fact some molecules like benzene are really stable because the moving of electrons causes energy to be continuously lost. We also drew the electrons moving around for some structures like nitrobenzene and learnt how these cause ortho para/ meta directing nature.

enter image description here

The two resonances I learnt about don't seem to be the same. My question is, what is the difference? Or is there a concept I misunderstood?

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    $\begingroup$ some molecules like benzene are really stable because the moving of electrons causes energy to be continuously lost This is wrong. Very wrong. The first description about ozone is correct. $\endgroup$ – bon Dec 5 '15 at 17:40

This is because the electrons dont actually jump between the atoms of the molecule, but rather the electron cloud density is even distributed through the resonating bonds. If atoms had to hold formal charges this would be very unstable for the electron count. In essence all of the resonant structures exist at the same time. This lack of formal bonding in resonace is why benzene is often drawn as a circle inside a hexagon. This explaination does involve a bit of hand waving, and ignores higher level inorganic, but I think it should provide the needed additional clairity.

  • $\begingroup$ Is it right to infer from your explanation that benzene is not stable because electrons move around and lose energy but because charge is more evenly distributed in the resonance structure? $\endgroup$ – Mahathi Vempati Dec 6 '15 at 3:34
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    $\begingroup$ Its a little more complicated than that but yes. It is worth noting though that benzene has a special kind of resonance called aromaticity which is far more stable than simple resonance. $\endgroup$ – A.K. Dec 6 '15 at 16:12
  • $\begingroup$ Follow up question: could you explain why a molecule that has more number of resonance structures is more stable? $\endgroup$ – Mahathi Vempati Dec 6 '15 at 16:35

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