Re: RE: AMMRL: 1H NMR of bromide compounds

From: Xianzhong Yan <yanxz_at_bmi.ac.cn>
Date: Tue, 10 Dec 2013 08:58:38 +0800 (GMT+08:00)

Hi, Sheng,

I think both 1.9 Hz and 0.9 Hz splittings are from 4-bond CH2, with two non-equivalentprotons.

Best,

Xianzhong

--
Xianzhong Yan, Ph.D.,Prof.
National Center of Biomedical Analysis
27 Taiping Road, Beijing 100039
P. R. China
-----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 Mon Dec 09 2013 - 15:02:45 MST