Hybridization of carbanion in rings

In summary, the conversation discusses determining the hybridization and number of pi electrons in a compound, as well as the concept of resonance structures and their relationship to stability. The theories of valence bond and VSEPR are also mentioned.
  • #1
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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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  • #2
mnmman said:
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.

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.
 
  • #3
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.
 
  • #4
Quantum Defect said:
draw resonance structures that move the pair of electrons around the ring

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?

DrDu said:
concept from valence bond theory

Does this theory have anything in common with VSEPR? My book only mentions VSEPR and nothing about valence bond theory
 
  • #5
mnmman said:
Does this theory have anything in common with VSEPR? My book only mentions VSEPR and nothing about valence bond theory
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.
 

1. What is the definition of hybridization in carbanions?

Hybridization in carbanions refers to the mixing of atomic orbitals to form new hybrid orbitals, which have different shapes and energies than the original atomic orbitals. This process occurs in molecules containing a negatively charged carbon atom, also known as a carbanion.

2. How does hybridization affect the reactivity of carbanions in rings?

Hybridization plays a crucial role in determining the reactivity of carbanions in rings. The type of hybridization, as well as the number and orientation of the hybrid orbitals, can influence the stability and reactivity of the carbanion. For example, sp3 hybridized carbanions are generally more stable than sp2 or sp hybridized carbanions.

3. What factors determine the type of hybridization in carbanions in rings?

The type of hybridization in carbanions is primarily determined by the number of bonds and lone pairs of electrons around the carbon atom. For example, a carbon atom with four bonds and no lone pairs will have sp3 hybridization, while a carbon atom with three bonds and one lone pair will have sp2 hybridization.

4. Can carbanions in rings exhibit different types of hybridization?

Yes, carbanions in rings can exhibit different types of hybridization, depending on the position of the negatively charged carbon atom within the ring and the surrounding functional groups. For example, a carbanion on a sp3 hybridized carbon in a cyclohexane ring can undergo a conformational change to become sp2 hybridized if it becomes a part of a conjugated system.

5. How does the hybridization of carbanions in rings impact their stability?

The hybridization of carbanions in rings can greatly influence their stability. Generally, carbanions with sp3 hybridization are more stable than those with sp2 or sp hybridization. This is because sp3 hybridization allows for greater electron delocalization and distribution of negative charge, leading to a more stable structure.

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