Sheng,
A mild Gaussian window function might reveal more splittings in the proton
spectrum.
Otherwise a COSY should show you which protons are responsible for the small
couplings.
I bet they are 4J couplings to the two non-equivalent CH2 protons.
Check this database to compare your spectral data on this compound:
http://sdbs.db.aist.go.jp/sdbs/cgi-bin/direct_frame_disp.cgi?sdbsno=4818
Best Regards,
Jürgen
_______________________________________________
Jürgen Schulte, Ph. D. Ph.: 607-777-4405 (G-14)
NMR-Specialist 607-777-4700 (B-2)
Binghamton University Fax: 607-777-4478
Chemistry Department
Binghamton, NY 13902-6000
schulte_at_binghamton.edu
http://chemiris.chem.binghamton.edu/staff/schulte
-----原始邮件-----
发件人: "Cai, Sheng" <sheng.cai_at_marquette.edu>
发送时间: 2013年12月7日 星期六
收件人: "ammrl_at_ammrl.org" <ammrl_at_ammrl.org>
抄送:
主题: 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 PM
To: 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 Tue Dec 10 2013 - 09:00:41 MST