Hi All,
Thank you so much for quick responses from many colleagues (Ion Ghiviriga,
Gabriel Gonzalez Ferrer, Daniel Holmes, Stephen Lynch, James Aramini,
David Vander Velde). The minor peaks are from one and two bonds J coupling
between 13C-19F. They are not symmetric to main peak because the main peak
is from 12CF3-12CH2-OH, and the splitting are from either 13CF3-12CH2-OH or
12CF3-13CH2-OH, but with different chemical shift from 12CF3-12CH2-OH due
to carbon isotope effect, so they are not symmetric to the main peak. Daniel
Holmes shared a great example about this posted by Glen Facey.
http://u-of-o-nmr-facility.blogspot.com/2012/10/isotope-effects-and-19-f-13-c-hmqc.html
Many thanks,
Weidong
From: main_at_ammrl.groups.io <main_at_ammrl.groups.io> On Behalf Of Ghiviriga,Ion
Sent: Wednesday, July 12, 2023 11:15 AM
To: main_at_ammrl.groups.io
Subject: Re: [AMMRL] Unexpected peaks of 19F NMR from CF3CH2OH
Hi Weidong, It is the C13 isotope effect on the F19 chemical shifts. The chemical
shift of the F19 bound to the C13 is in the middle of the peak 1 and peak 3. The
chemical shift of the F19 two bonds away from C13 is in the middle of peak 2
Hi Weidong,
It is the C13 isotope effect on the F19 chemical shifts. The chemical shift
of the F19 bound to the C13 is in the middle of the peak 1 and peak 3. The
chemical shift of the F19 two bonds away from C13 is in the middle of peak
2 and peak 4 which overlaps the main peak.
Best,
Ion
Ion Ghiviriga
Director of the Center for NMR Spectroscopy
University of Florida, Chemistry Department
Gainesville, Fl 32611-7200
Ph: 352-846-3001
From: main_at_ammrl.groups.io<mailto:main_at_ammrl.groups.io> <main_at_ammrl.groups.=
io<mailto:main_at_ammrl.groups.io>> On Behalf Of Weidong Hu via groups.io
Sent: Wednesday, July 12, 2023 1:33 PM
To: main_at_ammrl.groups.io<mailto:main_at_ammrl.groups.io>
Subject: [AMMRL] Unexpected peaks of 19F NMR from CF3CH2OH
Hi All,
I acquired 1D-19F NMR of CF3CH2OH dissolved in CDCl3/CD3OD(2:1 v/v) on CP TCI
700 H&F-C/N-D probe (without 1H decoupling), and the spectrum is very confusing.
In addition to main triplet peaks, there are three minor triplet peaks (about
0.5% of main triplet). The positions of minor peaks are not symmetric to the
main triplet, and thus should not come from natural abundance of 13C-19F J
coupling. It is reasonable to see four minor peaks generated from one and
two-bond J couplings between 13C-19F, but they should be symmetric to the
main peak. I don't know how to explain the observed spectrum. Any suggestions
as what is going on? The spectrum is attached below.
Thank you,
Weidong
Dr. Weidong Hu
Department of Immunology & Theranostics
Beckman Research Institute
1450 E. Duarte Rd., Duarte, CA 91010
Tel: 626 256 4673, Ext: 63416
Fax: 626 301 8186
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Received on Wed Jul 12 2023 - 12:55:57 MST