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We have an olefin, R1-CH=CH-R2 where proton resonances overlap. Is there a way to determine olefin isomer - E (trans) vs Z (cis) by NMR?

asked Apr 30 '10 at 13:36

Evgeny%20Fadeev's gravatar image

Evgeny Fadeev
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updated Apr 30 '10 at 13:36


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It is not clear whether if the overlap included the hydrogens directly attached to the double bond. If the protons attached to the double bond have well resolved resonances then the measurement of the coupling constant between these two hydrogen nuclei will allow you to distinguish the E and Z isomers. The trans isomer is expected to have a much larger coupling constant.

However, if the resonance overlap involves the resonances of the hydrogens directly attached to the double bond in R1-CH=CH-R2, then a spectral simulation and fitting program such as LAOCOON/PERCH may allow you to extract the relevant coupling constant.

A few relevant references are listed below:

J. Chem. Educ., 1990, 67 (3), p 235; Matthew Clark and Joseph S. Thrasher; LAOCOON PC: NMR simulation on a personal computer

LAOCOON3: Organic Magnetic Resonance Volume 13 Issue 4, Pages 277 - 278

http://www.perchsolutions.com/products/PERCHNMRSoftware.html.

A list of NMR software is available at http://www.spincore.com/nmrinfo/

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answered May 03 '10 at 22:38

Talluri%20Sekhar's gravatar image

Talluri Sekhar
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updated May 06 '10 at 08:48

Evgeny%20Fadeev's gravatar image

Evgeny Fadeev
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There are several methodolgies. See for instance,

Nolis, P.; Roglans, A.; Parella, T. IFSERF, an isotope-filtered SERF experiment for the precise measurement of proton-proton coupling constants between chemically equivalent protons. Journal of Magnetic Resonance. 2005, 173, 305-309.

also references therein.

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answered May 05 '10 at 12:55

Pau%20Nolis's gravatar image

Pau Nolis
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Thanks! Here is the paper url http://dx.doi.org/10.1016/j.jmr.2004.11.029 - Evgeny Fadeev (May 06 '10 at 08:45)

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For overlaped signals, you can use some experiments to solve this problem. One is the use of the technique CSSF where signals overlap with at least 2 Hz separation between them using selective excitation (ref.:P.T. Robinson et al., In phase selective excitation of overlapping multiplets by gradient-enhanced chemical shift selective filters. Journal of Magnetic Resonance 170 (2004) 97–103 link text). The other is the use of SELINCOR technique (1D version of HMQC experiment). Irradiatin the olefinic carbon, you will obtain the 1H spectrum via 1J CH correlation. (REF.: S. Berger., Journal of Magnetic Ressonance 81 (1989), 561-564 link text)

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answered Jul 10 '10 at 06:00

Cleber%20Barreto's gravatar image

Cleber Barreto
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updated Jul 10 '10 at 08:07

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