Acidity comparison: cyclopentadiene vs. fluorene

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waldonator
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Which would be the most acidic out of these two hydrocarbons and why?
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charco
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(Original post by waldonator)
Which would be the most acidic out of these two hydrocarbons and why?
The most acidic is the one that more easily loses the hydrogen ion leaving the conjugate base.

So, you are really asking which of the two has the most stable conjugate base.

If you draw both of the conjugate bases and look for the number of ways in which the negative charge can be delocalised around the structure, the one with the most resonance forms will be the most stable.
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waldonator
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(Original post by charco)
The most acidic is the one that more easily loses the hydrogen ion leaving the conjugate base.

So, you are really asking which of the two has the most stable conjugate base.

If you draw both of the conjugate bases and look for the number of ways in which the negative charge can be delocalised around the structure, the one with the most resonance forms will be the most stable.
So instinctively I feel the fluorene has the greatest number of resonance forms...if I was asked to draw its resonance structures, would I have to show the neg charge running through both phenyl groups, or would it be acceptable to just show it delocalised around one of them? Surely if you delocalised through both there would be many equivalent structures?
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charco
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(Original post by waldonator)
So instinctively I feel the fluorene has the greatest number of resonance forms...if I was asked to draw its resonance structures, would I have to show the neg charge running through both phenyl groups, or would it be acceptable to just show it delocalised around one of them? Surely if you delocalised through both there would be many equivalent structures?
That entirely depends on for whom you are carrying out the analysis. My feeling is that what you do in one aromatic ring could easily be doubled, but, hey, I'm just a bum.
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