Why I only obtain some peaks in the sildenafil HMBC 1H-15N?

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I am trying to obtain the 1H-15N-HMBC of sildenafil molecule in a BBI 400 MHz probe. I only detect the correlations between the H and N in the aromatic moiety (the pirazol part) but any signal from the piperazine part. I have tried to increase the delay time (to 20 sec), long-range filters (from 5 to 10 hZ) unsuccessfully. Why?

1H-15N

asked May 24 '13 at 09:20

Gohuma
3

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Hi Gohuma,

I think I have also seen this problem, I may still have the data somewhere so will attempt to find it. My memory is that exchange broadening of the proton signals in the piperazine part meant that the polarisation transfer was ineffective (signal decays completely in the relatively long transfer delay due to short effective proton T2). Look for the signals of the piperazine protons - are they rather broad? If so that may be the issue.

hope that helps!

link

answered May 27 '13 at 12:17

Pete Gierth
401

In case anyone's still reading this... I finally ran the experiment at 80 degrees in DMSO, and in the proton spectrum you see the piperazine protons sharpen up (you can see a splitting rather than just a broad lump). At this temperature you can see the correlations to the piperazine nitrogens. - Pete Gierth (Feb 25 '15 at 14:42)

0	You are right. The signals are broad,then, I am afraid I can not see them! Thank you. I can not post the NMR due to my "little karma". I would like... link answered Jun 03 '13 at 09:33 Gohuma 3

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1H-15N ×3

Asked: May 24 '13 at 09:20

Seen: 3,725 times

Last updated: Feb 25 '15 at 14:42

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