Anti-Aromaticity

[lakers2009]

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Why is E not anti-aromaticity? It's 4 pi and planar? Why is D anti-aromaticity? I can't figure out the explanation. A & B, follows Huckel 6 pi, thus aromaticity C, is 8 pi e- but non-aromaticity rather than anti-aromaticity

 

[hausee]

I was actually reviewing this part yesterday and got confused too. As i understand:

aromatic=ring+[available p orbit on every atom of the ring]+[4n+2 e-]
antiaromatic=ring+[available p orbit on every atom of the ring], but without [4n+2 e-]

So
A: has two atom with sp3 and no p orbit available even it has 4n+2 e-,=> neither aromatic nor antiaromatic
B: every atom has sp2 and 4n+2 e- =>aromatic
C: every atom has sp2 and not 4n+2 e- =>antiaromatic?
D: not sure about this.
E: not ring and not planner because it rotate along single bond.

Ps how do I know if there is H attach to C on this pictures?

correct me please

 

[americanpierg]

Why is E not anti-aromaticity? It's 4 pi and planar? Why is D anti-aromaticity? I can't figure out the explanation. A & B, follows Huckel 6 pi, thus aromaticity C, is 8 pi e- but non-aromaticity rather than anti-aromaticity

A is NOT aromatic, it's also NOT anti aromatic because its not conjugated. B is aromatic. C is NOT anti aromatic, becau'se its not planar. E is not a conjugated ring.

I thought D was aromatic too until I realized that the dots were radicals. If they were electrons, it would be armoatic. Each single radical electron occupies a p orbital, and each carbon is sp2 hybridized. Also, its a conjugated system. D is anti aromatic.

 

[chromosome21]

Why is E not anti-aromaticity? It's 4 pi and planar? Why is D anti-aromaticity? I can't figure out the explanation. A & B, follows Huckel 6 pi, thus aromaticity C, is 8 pi e- but non-aromaticity rather than anti-aromaticity

A is wrong cause it doesn't have conjugated pi electrons
B is wrong cause it's an "aromatic" compound (benzene)
C is wrong cause it has 8 pi electrons
D is RIGHT cause cause the rule of a compound being anti-aromatic is having a 4N pi electrons. Here, this compound does have 4 pi electrons in it.
E is wrong b/c it's not cyclic. It's not an aromatic compound.

 

[minotaur9]

The IUPAC criteria for antiaromaticity are as follows:[1]

1. The molecule must have 4n π electrons where n is any integer.
2. The molecule must be cyclic.
3. The molecule must have a conjugated pi electron system.
4. The molecule must be planar.

Hope this helps 🙂

 

[c3p]

how come C isnt planar, i thought it was sp2 hybridized....

 

[lakers2009]

thanks all

how come C isnt planar, i thought it was sp2 hybridized....

It buckle up like a taco supreme http://en.wikipedia.org/wiki/Conjugated_system

It is important to note that merely possessing alternating double and single bonds is not enough for a system to be strongly conjugated. Some cyclic hydrocarbons (such as cyclooctatetraene) do indeed possess alternating single and double bonds. Although the molecule may appear planar if one looks only at its chemical structure, it is in fact not, and typically adopts a "tub" conformation. Because the p-orbitals of the molecule do not align themselves well in this non-planar molecule, the electrons are not as easily shared between the carbon atoms. They can be still considered conjugated, but they are not considered antiaromatic (and also not aromatic; see Hückel's rule). Cyclooctatetraene would not be considered antiaromatic because it is not planar.

also pretty good link http://en.wikipedia.org/wiki/Antiaromatic

 

[americanpierg]

how come C isnt planar, i thought it was sp2 hybridized....

To be honest, I think it's far beyond the scope of what you need to know for the DAT. It's just one of those things you have to memorize. I found out that it wasn't planar from Topscore (or was it achiever).

I'm sure there's some rules behind why it isn't planar, but I don't know if anyone on here can tell you.

 

[slm266]

how come C isnt planar, i thought it was sp2 hybridized....

even tho they are sp2, I still believe it takes on this shape.
Correct me if i'm wrong.

 

[c3p]

To be honest, I think it's far beyond the scope of what you need to know for the DAT. It's just one of those things you have to memorize. I found out that it wasn't planar from Topscore (or was it achiever).

I'm sure there's some rules behind why it isn't planar, but I don't know if anyone on here can tell you.

yea i got it on top score, so i guess ill just memorize...thanks.

 

[c3p]

even tho they are sp2, I still believe it takes on this shape.
Correct me if i'm wrong.

nice work, i found out it was like that on wiki. thanks.