Dear all,
With the help from Neil and others from this community, I finally figured out
the 1D proton spectrum of this compound. Yes, this 0.9 Hz is from a long range
coupling, between H3 (4.62 ppm) and H6 (1.69 ppm). And H6 also has a 0.9 Hz
coupling to another peak. It is hard to see these small couplings on H6 because
the peaks are broad. I uploaded the raw data on Agilent Spinsight
https://spinsights.chem.agilent.com/login under group "Small Molecular NMR".
This molecule has lots of long range couplings and secondary patterns. It is
excellent for the teaching purpose. Please have a look if you are interested.
Thank you again for your help.
Sheng
________________________________________
> From: Cai, Sheng <sheng.cai_at_marquette.edu>
> Sent: Tuesday, December 10, 2013 4:11 PM
> To: ammrl_at_ammrl.org
> Subject: RE: RE: AMMRL: 1H NMR of bromide compounds
Hi all,
Thank you for your time. Most people suggest long range coupling. But my problem
is I don't see this 0.9 Hz from any other signal. I cannot find its coupling parter.
All other peaks show perfect coupling patterns (multiplicity), without this 0.9 Hz.
I am on a trip now. Once I get back to my office, I will upload the spectrum, so
you can see it more clear.
Sheng
> RE: AMMRL: 1H NMR of bromide compounds
Hi all,
Thank you all for your suggestion. We did some further investigation and found
two of our Br compound have isomers and caused the spliting.
But I still cannot explain the spectrum of one compound, ((1R)-endo)-(+)-3-Bromocamphor
(CAS # 10293-06-8). This compound was purchased from SigmaAldrich. The proton attached
to the bromocarbon (position 3) shows a doublet (4.6 Hz) of doublet (1.9 Hz) of
doublet (0.9 Hz) at 4.6 ppm (400 Hz instrument in CDCl3). The coupling of 4.8 Hz and
1.9 Hz can be easily assigned to 3-bond H-H coupling and long range coupling, respectively.
But I have no idea where the 0.9 Hz splitting come from. None of rest protons show this
0.9 Hz coupling. I can perfectly fit the entire spectrum using the measured J coupling
and chemical shifts, except for the 4.6 ppm one. Thus, I am sure this 0.9 Hz is not a
coupling. It comes from different isomers.
The SigmaAldrich catalog says this compound is a sum of enantiomers. I thought all
enantiomers should give same NMR spectra, if the compound they sold me is pure
(no 3-bromocamphor, CAS # 76-29-9). So, I was left with only one choise, Br isotope
effect. I looked through literature and cannot find any information on Br effect on
1H chemical shifts.
Did I miss something? Thank you very much.
Sheng
________________________________
From: Cai, Sheng
Sent: Tuesday, November 26, 2013 2:40 PMTo: ammrl_at_ammrl.org<mailto:ammrl_at_ammrl.org>
Subject: 1H NMR of bromide compounds
Hi all,
I found some bromine-containing organic compounds showing strange splitting
patterns in proton NMR. I cannot explain these splittings (usually 1-2 Hz)
using any long-range spin-spin coupling. I suspect they may come from Br79/81
isotope effect. Has anybody observe this before ? A link to references will
be highly appreciated. Thank you.
Sheng Cai
Marquette University
Received on Wed Dec 18 2013 - 06:19:55 MST