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Hybridization of carbanion in rings

  1. Jan 28, 2015 #1
    So this question asked me to determine whether this compound was aromatic, antiaromatic, or nonaromatic and also asked how many pi electrons there were. I figure since there are four groups of electrons the carbanion is sp3 hybridized and I think I'm correct because that is what this thread says.

    https://www.physicsforums.com/threads/question-regarding-hybridization-of-carbon.256312/

    But apparently the lone pair on this carbanion in this specific compound lies in a p-orbital (as opposed to sp3)? thus making this carbanion sp2 hybridized? for a total of 8 pi electrons. This makes no sense to me any help would be greatly appreciated.
     

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  3. Jan 28, 2015 #2

    Quantum Defect

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    In this particular compound, you can draw resonance structures that move the pair of electrons around the ring. Each of the carbons has one hydrogen bonded to it, and the charge is delocalized around the ring. The only way that this could happen is if each carbon is sp^2.

    Remember that Lewis structures are approximations. How about Benzene? The single Lewis structure would predict alternating short and long C-C bonds. The measurement reveals six identical bonds with bond length that is intermediate between C-C and C=C. In the present case, the Lewis structure is incorrect because it predicts a lone pair (with negative charge) on a single carbon -- the lower energy form is with the charge spread out over the entire ring, which is what the resonance structures would predict.
     
  4. Jan 29, 2015 #3

    DrDu

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    Usually this kind of questions is not about hybridization, which is a concept from valence bond theory, as in school aromaticity is introduced using molecular orbital theory. The pi orbitals are formed from p orbitals on the atoms.
     
  5. Jan 29, 2015 #4
    ok I can see it now that was very helpful, so if you draw the resonance structures and they end up looking the same but rotated, is that a way you can tell they are especially stable?

    Does this theory have anything in common with VSEPR? My book only mentions VSEPR and nothing about valence bond theory
     
  6. Jan 30, 2015 #5

    DrDu

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    Yes, VSEPR is a scheme that was derived from valence bond ideas, although it is highly simplified.
    However terms like hybridization or resonance are from valence bond theory and not VSEPR.
     
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