Hello,
I had similar problems with NMR of amines in CDCl3. CDCl3 normally contains
some DCl, and it causes protonation of amine, which is then in chemical exchange
with unprotonated one. This chemical exchange causes peaks broadening. This
was fixed by filtering CDCl3 through basic alumina.
Another problem is that CDCl3 in the presence of some amines becomes photolabile,
and again forms DCl. This happens immediately under sunlight (i.e. UV light) and
slowly (15 min to a few hours) under visible light. So, for me light protection
did help.
Regards,
Volodymyr Semeniuchenko
University of Ottawa
________________________________
> From: main_at_ammrl.groups.io on behalf of Andre Dallmann via groups.io
> Sent: October 1, 2025 11:04 AM
> To: main_at_ammrl.groups.io <main_at_ammrl.groups.io>
> Subject: Re: [AMMRL] Help Needed: Broad/Missing ¹³C NMR Signals
Dear Muhammad,
looks to me like you are dealing restricted molecular motion (e.g.
Pi-stacking) and/or a second species due to chemical exchange
(protonation and/or different stereoisomers due to the nitrogen centre
and its lone pair). The latter you can deal with by switching solvent
and controlling the pH, the former via dilution and elevated temperature
Chemical exchange:
In the first case KB-P19-NOâ‚‚ with the acidity of CDCl3, which might give
you at least partly a protonated species (the central Nitrogen in the
molecule should probably protonate pretty easily), which - depending on
what timescale this protonation is happening - will give you either just
a second set of signals or broad lines (as well).
The second molecule might have the same problem, with protonation of
either central nitrogen, the molecule will become non-symmetrical and
you will get broad lines depending on the exchange rate.
Best, André
--
Dr. André Dallmann
Leiter der NMR-Abteilung
Email: andre.dallmann_at_chemie.hu-berlin.de
Raum: 0'103
Telefon: 82952
Handy: 01797657855
Adresse:
Humboldt Universität zu Berlin
Institut für Chemie
AG NMR
Brook-Taylor-Str. 2
12489 Berlin
Deutschland
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Received on Wed Oct 01 2025 - 08:18:22 MST