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I want to know which are the most stable furan resonance structures. I know that structure number 1 is the most stable, but which one comes after?

Resonance structures of furan

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  • $\begingroup$ 2/5 and 3/4 are identical $\endgroup$
    – Radu
    Jun 1, 2012 at 21:53
  • $\begingroup$ And do you want to know which is more stable in order to predict properties like reactivity? Or is it just a question for it's own sake? $\endgroup$ Jun 1, 2012 at 23:38
  • $\begingroup$ I want to ask about which one is more stable thus less reactive ? also which one has the higher charge separation and how does it affect the stability ? $\endgroup$ Jun 2, 2012 at 2:48
  • $\begingroup$ I think your structures 2–5 have a problem as they are lacking a negative charge to balance the positive charge… furan is a neutral molecule, as indicated in your structure 1. $\endgroup$
    – F'x
    Jun 3, 2012 at 20:34
  • $\begingroup$ There are no such things as more or less stable resonance structures. See also What is resonance, and are resonance structures real? $\endgroup$ Nov 12, 2018 at 20:49

1 Answer 1

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A quick post so you can get started on thinking about this.

Remember, resonance is just a model. The electrons are delocalized all the time; the furan does not morph back and forth among the various structures.

You can do a "formal" evaluation of which resonance forms have the most contribution to the structure by looking at formal charges, and there are rules to help you decide, from the formal charges, which resonance forms are most important.

If you're looking at reactivity, the property you're interested in may not be that the one that is "more stable is less reactive". What you might look at instead, is the consequences of attack at the 2 and 3 position, look at the stability of the intermediates formed...a more stable intermediate would tend to drive the reaction along that path.

After looking at these ideas, feel free to come back with specific questions.

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  • $\begingroup$ I mean i want to know which is more preferable .. especially between structure no. 2 and 3 ? $\endgroup$ Jun 4, 2012 at 12:49
  • $\begingroup$ Evaluate them by the rules for "formal charges" and that answer that part of the question. $\endgroup$ Jun 4, 2012 at 18:09
  • $\begingroup$ "Remember, resonance is just a model." - +1 for this. More explicitly: we use resonance to deal with the limitations of using Lewis structures to represent molecules that exhibit electron delocalization. $\endgroup$
    – user95
    Jul 7, 2012 at 17:24

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