proton NMR

[sara...@gmail.com]

I am having trouble understanding the H NMR for 5-norbornene-2,3-
dicarboxylic anhydride (to see it, please see:
http://www.aist.go.jp/RIODB/SDBS/cgi-bin/direct_frame_top.cgi?lang=eng).

To begin with, I don't understand why H's D and E are labelled as non-
identical hydrogens, when you only see one peak for D/E on the
spectrum. I am also unclear as to why you can't see the difference
between B and C on the spectrum (they are merged into one peak, when
it seems that B is closer to the electronegative =O than C, and thus
more deshielded).

Any help would be appreciated.
Thanks

[Micha? Sobkowski]

Dnia 4/11/2007 4:58 PM, sara...@gmail.com napisa?(a):

> http://www.aist.go.jp/RIODB/SDBS/cgi-bin/direct_frame_top.cgi?lang=eng).
>
> To begin with, I don't understand why H's D and E are labelled as non-
> identical hydrogens, when you only see one peak for D/E on the
> spectrum.

Are you sure it is one signal? Why is it quartet then? :-)

Actually, these are two overlapped triplets (or rather pseudo-triplets
as the theoretical pattern is more complicated; on high-resolution
spectrum you should probably see more signals)

> I am also unclear as to why you can't see the difference
> between B and C on the spectrum (they are merged into one peak, when
> it seems that B is closer to the electronegative =O than C, and thus
> more deshielded).

Hint: cyclopentene ring.

Michal