I would not be surprised to see two long-range couplings: both the W and the inverted "zig-zag" protons geminal to each other. If they're shift dispersed, you might have the chance to see these fine splittings amid the expected large geminal doublet.
-Jack
Sent from my iPad
On Dec 6, 2013, at 11:59 AM, "Cai, Sheng" <sheng.cai_at_marquette.edu> wrote:
> 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 - 15:01:29 MST