[madscientist]

Hi all,

I Have a question I need to answer and was wondering what principles I should be looking at to answer it. All I can think of is that is has somthing to do with resonance forms of this compound?

The question reads as follows.

Q.) Explain why tetra(dimethylamino) cyclobutadiene dication is stable?

Any help is appreciated,

Cheers

Madscientist

[Custos]

Why is the cyclopentadiene anion stable? How many pi electron are there? Think about Hückel's rule. look up aromaticity...

[madscientist]

Ok, so the cyclopentadiene anion is a 6 pi electron system and therefore aromatic by huckels criteria. So the cyclopentadiene anion is stable due to the aromatic stabilisation effect yes?

So if i find that the tetra(dimethylamino) cyclobutadiene dication is aromatic, (2,6,10,14...pi electrons), is that enough to explain the stability of this compound?

Thanks for your help,

cheers

Madscientist

[Custos]

Yes, that's correct.

[english]

By first glance the cyclopentadiene anion does not look like it's aromatic.  In fact, it looks as if it's antiaromatic (or not aromatic—a compound would rather be not aromatic than antiaromatic).

If you look at its resonance structures, like you mentioned, the anionic pair of electrons is delocalized across the entire cyclic plane, and thus each carbon is at some point sp² hybridized.  This means there is actually a cyclic pi cloud.  This would follow Huckel's rule, that there are 4n + 2 pi electrons, and we can therefore conclude that cyclopentadienyl ion is aromatic.

[madscientist]

Thanks for your help guys.

Cheers,

madscientist

[AhmedEzatAlzawalaty]

  i think it is very simple .in cyclobutadiene anion teh Compond is
1-Cyclic
2-planar SP2
3-The pi electron system is continous and not interrupted
4-It obeys Huckle Rule 4n+2=6
From first sight it is aromatic
.

[madscientist]

On the original question, as to why the tetra(dimethylamino) cyclobutadiene dication is stable.

I understand that its stable because its aromatic, but ive found another answer which im told is right but i can't understand why, the answer given is below:

"Cyclobutadiene dication is a 4n+2 (n=0) pi system. From the graphical method, the only bonding orbital is doubly occupied.  In addition the four nitrogen lone pairs on the amino groups can stabilise the positive charge."

The first part of this answer makes sense because it basically saying that the compound is aromatic with its lowest energy orbitals doubly occupied, therefore stable.  What i dont get is how the nitrogen lone pairs can act to stabilise the positive charge, the way im seeing it is if the lone pairs were to do this the compound would not be aromatic.  Can anyone please explain this answer to me.

[madscientist]

Can anyone see the picture i attached in the last post?

[Borek]

Picture OK.