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Help! I'm Taking Organic Chemistry!
NMR Spectrum 
27th-Apr-2009 04:02 pm
I've been trying to figure out these NMR readings of an aldol (alpha beta unsaturated carbonyl compound), and I can't seem to get the structure. To make matters more difficult, my teacher didn't supply me with the chemical formula...just that the aldehyde has no alpha hydrogens and is aromatic.

Here are the readings...and with my interpretations that I've come up with.

7.4 doublet 2H (para substituted benzene)
7.2 doublet 2H (para substituted benzene)
6.9 singlet 1H (double bond)
2.5 singlet 3H (methyl group either next to carbonyl or double bond)
2.1 singlet 3H (methyl group either next to carbonyl or double bond)
1.9 septet 1H (hydrogen in between these two identical methyl groups)
0.9 doublet 6H (two identical methyl groups)

But for some reason, I cant structure and combine it all correctly to make it an actual product.

Your help is greatly appreciated.
27th-Apr-2009 08:36 pm (UTC)
I think you're almost there. Based on the aromatic shifts and integrations, a para substituted benzene ring makes sense.

Now, looking at your most upfield peaks, you see a single hydrogen between two identical methyls. Since that H doesn't have any extra splitting, I'd stick it on the aromatic ring.

That only leaves the two methyls and vinyl hydrogen. Now, since you don't have any alpha hydrogens and there aren't any aldehydes, that vinyl H is probably beta to the carbonyl. (Since aldols produce alpha, beta unsaturated carbonyls.)

Now you only have to think about where those methyls can go.

If you have access to ChemDraw, ChemSketch, or some other structure-drawing program, those can usually predict NMR spectra, so you can check yourself.

Good luck!

27th-Apr-2009 09:09 pm (UTC)
thanks for the help. I just can't figure out if the two benzene rings are para to each other? or if they are not connected to each other. is there anyway to tell?
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