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

From: Xianzhong Yan <yanxz_at_bmi.ac.cn>
Date: Thu, 19 Dec 2013 09:25:52 +0800 (GMT+08:00)

I really hope to see a COSY spectrum which will make things simple.

Xianzhong

--
Xianzhong Yan, Ph.D.,Prof.
National Center of Biomedical Analysis
27 Taiping Road, Beijing 100039
P. R. China
>
>  "Cai, Sheng" <sheng.cai_at_marquette.edu>
> "ammrl_at_ammrl.org" <ammrl_at_ammrl.org>
>RE: RE: AMMRL: 1H NMR of bromide compounds
>
> 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 Spin
> sight 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 PM
> To: 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 - 15:30:09 MST