Thread: HNMR chemical shift characteristic?
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Unread 01-09-2005, 01:40 AM
Supertramp_82 Supertramp_82 is offline
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Default HNMR chemical shift characteristic?
I'm not sure what is confusing you about cyclopentadiene. The methine (CH) protons are part of alkenes and the methylene (CH2) is doubly allylic, next to two alkenes. Anisole is an electron-rich aromatic molecule. By resonance, electron density is donated to the ortho and para positions shifting those protons upfield. The meta positions don't have much of a different electron density than benzene, so they are near 7.27. The opposite effect should be observed in acetophenone, since the ketone will withdraw electron density from the meta positions, and not really from the ortho/para positions. Hope that helps. Something else that you might consider about cyclopentadiene is the fact that the cyclopentadienyl anion is aromatic, so the bonds to the methylene protons may be adjusted so there is partial negative charge on that carbon.

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