Hi Muhammad,
These appear to be dynamic effects, so interconversion between conformers or
whatever etc., and nothing to do with acquisition parameters (as evidenced
by the DMSO sample of KB-P19-NO2 and ethyl benzene). To counteract the dynamic
effects and move from the intermediate state between slow exchange (separate
signals for the interconverting species) and fast exchange (an averaged spectrum
of the interconverting species) one can increase the rate of interconversion
by raising the temperature. Unfortunately CHCl3 is limited since its boiling
point is only 60 C (you can use pressure tubes to go higher of course). Another
approach is to reduce the frequency difference in the exchanging spins by going
down in field if you have access to a lower field instrument.
Regards,
K. Klika
________________________________________
> From: Muhammad Adil Raees via groups.io
> Sent: 01 October 2025 17:38:00
> To: 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 - 08:04:39 MST