I think that you are probably not getting enough molecular motion to average
out the anisotropic interactions. The molecules are large and there could
be pi-stacking.
You could try more dilute solutions or raising the temperature.
I hope that helps.
Jay
________________________________
> From: main_at_ammrl.groups.io on behalf of Muhammad Adil Raees via groups.io
> Sent: Wednesday, October 1, 2025 9:38 AM
> To: main_at_ammrl.groups.io <main_at_ammrl.groups.io>
> Subject: [AMMRL] Help Needed: Broad/Missing ¹³C NMR Signals
Hi all,
I’m seeking advice on improving ¹³C NMR spectra that show
broad or missing signals.
Sample KB-P19-NO₂ in CDCl₃ had broad/missing signals, but in
DMSO it became sharp with good intensity.
Sample HY-VI-135-HH in CDCl₃ is also showing broad/missing signals
and is insoluble in Acetone, DMSO, and MeOD. We specifically want to improve
the ¹³C signals for HY-VI-135-HH.
For these experiments, I used zgpg or zgpg30 pulse programs. NMR instrument
is working fine — standard tests in CDCl₃ (ethyl benzene)
show all signals clearly. The FID files and molecular structures are attached
for reference.
It seems sample-related, but I’m wondering:
1. Could the broad signals be due to acquisition parameters?
2. Are there ways to improve the signals for HY-VI-135-HH?
3. Could the broadening be inherent to the molecule’s chemistry?
Any tips or shared experience would be greatly appreciated!
Thanks,
--
Muhammad Adil Raees, Ph.D.
Manager NMR Facility
The Central Laboratory
Syed Babar Ali School of Sciences and Engineering
Lahore University of Management Sciences
Opposite Sector-U, D.H.A. 54792, Lahore
+92-330-2866755
adil.raees_at_lums.edu.pk
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Received on Wed Oct 01 2025 - 08:00:29 MST