aromatic compound concept help!

[lamborghiniMD]

Can a compound be aromatic with triple bonds? Let's say a compound has 6 sides, but 3 sides are double bonds and 3 sides are triple bonds (in an alternating fashion).
I can't draw it here, but i hope you get the picture lol.

Also, what about cyclooctatrieneyl dianion and dication? This compound has 3 double bonds, but then has either a 2+ or a 2- charge

Thanks!

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[cheesier]

You would be violating the octet rule.

 

[lamborghiniMD]

No, the way it is drawn it isn't violating the octet rule. It sucks because I can't show you it.

 

[cheesier]

No, the way it is drawn it isn't violating the octet rule. It sucks because I can't show you it.

You said 3 triple bonds and 3 double bonds in a six membered ring which would indeed be a violation of the octet rule, because you would have 3 bonds to a member on one side and 2 on the other (if you are alternating double and triple bonds) in which case you would have 5 bonds total.

 

[lamborghiniMD]

nvm i figured it out. Aromatic compounds can have triple bonds as long as it doesn't violate the Hukel Rule, because a triple bond has 4 pi electrons (whereas double bonds have 2 pi electrons)

 

[Cptn Loko]

Aromatic compounds can have triple bonds, however only one of these pi bonds contribute to the Huckel Rule calculation because the second pi bond will not be in the same plane as all the other pi bonds.

The way I understand your description of the molecule, as 1 ring with alternating double and triple bonds, there will be a total of 12 pi electrons eligible for the Huckel rule, thus this compound would not be aromatic. It would probably be one weird compound though.

The cyclooctatrieneyl dianion and dication would be aromatic, since resonance is possible and they meet the Huckel rule.

Would love to know what review book you got this from

 

[lamborghiniMD]

Aromatic compounds can have triple bonds, however only one of these pi bonds contribute to the Huckel Rule calculation because the second pi bond will not be in the same plane as all the other pi bonds.

The way I understand your description of the molecule, as 1 ring with alternating double and triple bonds, there will be a total of 12 pi electrons eligible for the Huckel rule, thus this compound would not be aromatic. It would probably be one weird compound though.

The cyclooctatrieneyl dianion and dication would be aromatic, since resonance is possible and they meet the Huckel rule.

Would love to know what review book you got this from

Actually, I am taking Advanced Organic Chemistry and it was a homework question. My professor loves teaching us basic concepts but then testing us on harder concepts and rare exceptions. Fun stuff...

 

[lamborghiniMD]

found it! Just picture the central cyclic compound alone and ignore the benzene rings attached to it.

C12H6 and it has a total of 3 double bonds and 3 triple bonds