Explain D6h Symmetry of C6O6 2- Anion in "Inorganic Chemistry" Huhney

[telethrow]

I am trying to explain why an anion C6O6 2- would have the symmetry D6h. The problem gives you all of the IR and Raman absorptions and asks to explain why D6h is the proper symmetry for C6O6 2- anion.
Do you use character tables to figure this out? Or do I really have to go through the whole process of finding the irreducible set from the reducible set?
Please Help! I have been doing this for 5 hours!
anything will be greatly appreciated.

For you reference the problem is 3.25 in "Inorganic Chemistry" written by Huhney(sorry if i spelled your name wrong)

 

[gravenewworld]

Well I haven't done point group problems in about 5 years, but I will try to help you as best as possible.I assume by C6O6 2- you are talking about dianion of rhodizonic acid

http://www.tokyokasei.co.jp/common/img-structure/R0058.gifI think what is happening is that the enolate ion tautomerizes to the keto form. If you draw the flow of electrons you will see that the double bond would be resonating throughout the whole ring. I'm guessing it would be almost like a benzene ring with 6 O's attached to it.

Now have you ever used a point group symmetry table before like the one below?

http://www.poshusta.chem.wsu.edu/GroupTheory/FlowChart.htm

Just follow the questions and you should get the right symmetry in the end.

Assuming the double bond resonates throughout the whole molecule

Is it linear? No, go to the right

Does it have two or more Cn axes with n>2? No, go down

Does it have a rotation axis Cn? Yes (the one perpendicular in the center), go to the left

Select the biggest n (here it would be n=6 for the perpendicular axis to the center of the molecule), are there n C2 axes perpendicular to C6? Yes, all the axes through each O atom in the plane of the molecule and through each side. Is there a reflection plane perpendicular to C6? Yes. The end result by following the chart gives you D6h symmetry. Like I said, it has been a long time since I have done this stuff, so I am not 100% if I am right.

 

[chemisttree]

I am trying to explain why an anion C6O6 2- would have the symmetry D6h. The problem gives you all of the IR and Raman absorptions and asks to explain why D6h is the proper symmetry for C6O6 2- anion.
Do you use character tables to figure this out? Or do I really have to go through the whole process of finding the irreducible set from the reducible set?
Please Help! I have been doing this for 5 hours!
anything will be greatly appreciated.

For you reference the problem is 3.25 in "Inorganic Chemistry" written by Huhney(sorry if i spelled your name wrong)

Huheey. GNW has you covered...