[kriggy]

In a situation I have an acidic proton, is it possible for it to integrate for higher value? For example, having acidic OH proton, could it be possible for it to be seen as 2 or even 3 protons?

edit:
one more:
in my HMQC spectra i should see C-H interaction -> which proton in bonded to which carbon right? What does it mean, that I see crosspeak from one hydrogen to two carbons?

[TheUnassuming]

For the acidic proton, it should only integrate lower if anything due to exchange.  Where is the acidic proton coming?

HMQC should be the direct C-H bond interaction.  Are the interactions you see equal in signal strength?  The proton signal is only integrating to one I'm assuming? 

[kriggy]

I was thinking its from OH group but HMQC says it is bonded to carbon (and it is also the proton with 2 interactions) it looks like methyl but I have no idea where that came from. The molecule has methyl ester in it but the metyl is much lower about 1,7ppm
The crosspeaks look like this:

[TheUnassuming]

The one interaction is much stronger than the other.  Could you have another proton from a trace impurity buried under that proton peak? 

[kriggy]

I dont know, HPLC showed only one peak and the NMR shifts dont match any solvent used in the reaction. I guess it is possible but fail to see what could be the impurity

[Irlanur]

In HMQC you basically have to choose a value for the J-Coupling, so it's also possible that you just have an unusually large coupling to a carbon which is not a direct neighbour.

[TheUnassuming]

^this.  I just looked at some old HMBC data I have, and when I jack up the intensity I start to see other signals showing up for the same proton.  When I decrease the intensity of the HMBC signal though, it cleans up again and just shows the direct correlations.

[Irlanur]

"in principle" an HMBC is simply a low-pass filtered HMQC. There is simply no "hard" criterion that distinguishes directly and indirectly bound nuclei (from a J-coupling point of view).

[Babcock_Hall]

I must be misunderstanding something.  I don't see how a methyl group on a methyl ester could have a chemical shift of 1.7 ppm.

[kriggy]

hm good point, could it be the one at 3,75? I thought at first that it might be residual methanol but it doesnt seem right either (it doesnt match chemical shifts)

[Babcock_Hall]

Yes, that sounds about right.  Hans Reich has two nice tables of methyl group chemical shifts.  Scroll down the list at the left of this page:
http://www.chem.wisc.edu/areas/reich/handouts/nmr-h/hdata.htm

There is also a good paper on the chemical shifts of various common impurities in many deuterated solvents.  If you don't have that paper, I can find the reference.

[kriggy]

Thanks. I have that paper i was looking through those table several times but nothing matched the peaks Possibly my suggested structure is wrong ... I will talk to my supervisor tommorow maybe he will be able to see something im missing.