jemmiez
Registered: 10/25/09
Posts: 2
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Reply with quote | #1 |
The answer for the problem states that a cyclopentadienyl cation cannot be aromatic because it has only four pi electrons. However on p53 of the lecture supplement, the same molecule is used as an example under the point "closed loop p orbitals do not have to be occupied" to predict aromaticity. I also believe during lecture, prof Hardinger stated that resonance makes it so that the p orbital is not always unoccupied. Could someone clarify whether the molecule is actually aromatic or not? |
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sharonhu
Registered: 10/25/09
Posts: 4
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Reply with quote | #2 |
If you look at Chapter 15 (Benzene and Aromaticity), page 690 in the Vollhardt textbook, it explains that the cyclopentadienyl cation IS aromatic. The figure on the top of pag 691 shows that cyclic delocalization results in an aromatic structure with a negative charge spread over all 5 carbon atoms.
During lecture, I guess that Professor Hardinger meant that the unoccupied p orbital doesn't matter because of this cyclic delocalization.
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sharonhu
Registered: 10/25/09
Posts: 4
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Reply with quote | #3 |
Oh sorry that's a cation and not an anion! I'm not sure about whether it is or isn't aromatic, then. Sorry!
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jemmiez
Registered: 10/25/09
Posts: 2
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Reply with quote | #4 |
Oh wait, on same page of the book it also says "the cyclopentadienyl cation, a system of four pi electrons, can be produced only at a low temperature and is extremely reactive." I think the anion and not the cation qualifies as aromatic because it meets the conditions of Huckel's rule (4(1)+2) and has cyclic delocalization, whereas the cation has 4 e- and does not meet the requirements of Huckel's rule. |
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