Can We Use Huckel's Rule to Determine Aromaticity in 1,4-Benzoquinone?

[warenzeichen]

I am not sure how to use Huckel's rule to determine whether this compound is aromatic or not. It seems that inside the ring, there are only 4 pi electrons, and can the e- between C and oxygen move towards the ring?

 

[alxm]

can the e- between C and oxygen move towards the ring?

I'll give you a hint: They can't.

 

[warenzeichen]

when we count the no of pi e- , don't we consider the "possible resonance" structure?
Also, can we say this is a "fully delocalized" system?

 

[chemisttree]

Read http://www.rsc.org/delivery/_ArticleLinking/DisplayArticleForFree.cfm?doi=a903116b&JournalCode=P2" and see if it clears it up.

Search using the term "aromatic" using the 'find' feature of Acrobat.

 

[warenzeichen]

but for C=O , is it possible for us to draw as -C-O+ for prediction( although C is less electronegative than O)
for molecules with alternative resonance structure, do we need to consider all ?

 

[DrDu]

Hueckels rule is derived from MO theory, why do you want to count resonance structures then?

 

[warenzeichen]

so it is really inside the ring?

 

[DrDu]

Certainly to some degree. But aromaticity is not a totally well defined concept and Hueckels rules can sometimes be misleading. What about a diamagnetic ring current? NMR shifts of the Carbons and Hydrogens? Are there any experimental results?

 

[warenzeichen]

I wasn't anticipated to use extensive mathematics to explain simple molecules in intermediate organic chemistry courses. I think Huckel's rule is sufficient to explain them. But there are tautomers / one of the resonance structures . Hence, it is important to consider the structure to see if one of them got aromaticity in one structure (e.g. keto-enol tautomerism)


anyway, the compound is not aromatic.

 

[chemisttree]

I wasn't anticipated to use extensive mathematics to explain simple molecules in intermediate organic chemistry courses. I think Huckel's rule is sufficient to explain them. But there are tautomers / one of the resonance structures . Hence, it is important to consider the structure to see if one of them got aromaticity in one structure (e.g. keto-enol tautomerism)


anyway, the compound is not aromatic.

If you were to produce the correct tautomer, you would have a zwitterion where the formal charges were on the oxygens. In that case the ring itself would be aromatic. But if you consider the ground state, it isn't. That zwitterion is waay higher in energy than the rather modest aromatic stabilization energy you get as a result of shuffling the electrons into just the right locations.