Bromine isotope effects are expected to be very small, of the order of a
few ppb. Must be long-range 1H-1H couplings. The reason why you do not
see the 0.9 Hz splitting on the other proton is that there are other
small couplings of similar order of magnitude on the proton coupled to
CHBr. If you run some homonuclear decoupling experiments or COSY
optimised for long-range couplings (was COSYLR in bruker library before)
you may find the proton responsible for the 0.9 Hz splitting.
Dr Abil E Aliev
Department of Chemistry, University College London
20 Gordon Street, London WC1H 0AJ
Telephone: +44 (0) 20 7679 4616
Fax: +44 (0) 20 7679 7463
E-mail: A.E.Aliev_at_ucl.ac.uk
http://www.ucl.ac.uk/nmr
http://www.ucl.ac.uk/chemistry/staff/fellows/abil_aliev
On 10/12/2013 19:00, Novruz Akhmedov wrote:
>
> Dear Yan,
>
> *Usually cyclic (bi) compounds such bicycle [2.1.1] hexane reveal in
> their 1H NMR spectrum long-range (4JHH) couplings. The magnitude of
> 4JHH are in this range: 0.5 to 8 Hz . Even the magnitude of 4JHH in
> bicycle[1.1.1]pentane is so high (10 and 18 Hz).*
>
> *Nowadays using the NMR techniques it is very easy to determine all
> nJHH (n=2,3,4,5,6 etc) .*
>
>
> *I certainly believe that coupling of 0.9 Hz observed in
> *3-Bromocamphor *is 4JHH.*
>
> **
>
> *Thanks,*
>
> *Novruz*
>
> Novruz Akhmedov, Ph.D.
>
> Director of NMR Facility
>
> Web page*:****http://nmr.wvu.edu/*
>
> West Virginia University
>
> Department of Chemistry,
>
> 217 Prospect St., Clark Hall, Morgantown WV, 26506
>
> Phone: 304 293 0918
>
> 304 293 5366
>
> 303 293 0995
>
> *From:*Xianzhong Yan [mailto:yanxz_at_bmi.ac.cn]
> *Sent:* Monday, December 09, 2013 7:59 PM
> *To:* Cai, Sheng
> *Cc:* ammrl_at_ammrl.org
> *Subject:* Re: RE: AMMRL: 1H NMR of bromide compounds
>
> 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
> <mailto: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 <mailto:ammrl_at_ammrl.org>" <ammrl_at_ammrl.org
> <mailto: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 <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 11 2013 - 08:23:03 MST