Couldn’t help putting on my organic chemist hat. The structure is a
substituted triphenylamine Ph3N. The pKa of Ph3NH+ is-3.0, that of a very
strong Brønsted acid. This means the free amine is an exceedingly weak
base (due to extensive lone pair electron delocalization into the Ph rings
and unlikely to be protonated, except by the strongest acid. That doesn’t
mean there is not exchange with trace HCl , but not to the extent of, say, a
trialkylamine, R3N.
Ted M.
`
On Oct 1, 2025, at 11:51 AM, Platz Hirsch via groups.io wrote:
Dear Adil,
sorry for answering to Clemens contribution. Accidentally I delete your original contribution.
Looks like acidic CDCl3. There is a simple, but time consuming method to get it acid free.
Add a tiny amount (maybe 10 microgram) of silver oxide directly into the NMR
tube and shake it for 2 …3 hours.
An ultrasonic bath is fine.
No need to remove the silver oxide. This doesn’t disturb shimming.
If you do this procedure careful, you can see the CH-OH coupling within methanole
dissolved in CDCl3.
Greetings
Rainer
> Von: main_at_ammrl.groups.io <main_at_ammrl.groups.io> Im Auftrag von Anklin, Clemens via groups.io
> Gesendet: Mittwoch, 1. Oktober 2025 17:24
> An: main_at_ammrl.groups.io
> Betreff: Re: [AMMRL] Help Needed: Broad/Missing ¹³C NMR Signals
Hi Muhammad
I have two suspicions. One is dynamics. It could be that there is molecular
motion in CDCl3 that is happening on a different time scale in DMSO.
The other is that the HCL that often is present in CDCl3 causes issues with
the molecule. From the chemical shifts I suspect that the molecule contains
nitrogens. That can lead to equilibria between protonated and deprotonated
sites.
Try filtering the CDCl3 over activated basic alumina. The alumina has to be
dried very well other wise you end up with water in the sample.
With best regards
Clemens
On 10/1/2025 10:38 AM, Muhammad Adil Raees via groups.io wrote:
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<mailto:adil.raees_at_lums.edu.pk>
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Received on Wed Oct 01 2025 - 17:54:51 MST