The cross-peaks highlighted in yellow in the top panel of the figure are expanded in the bottom panel. Black contours are positive and red contours are negative. The panel on the bottom left shows the cross-peaks for AX and BX. In the case of the AX cross-peak, the line drawn through the cross peak has a positive slope indicating that the passive couplings JAB and JBX are of opposite sign. The line drawn through the BX cross peak also has a positive slope indicating that the passive couplings JAB and JAX are of opposite sign. From this we can deduce that JAX and JBX are of the same sign. The panel on the bottom right shows the cross-peak for AB. In this case, the line drawn through the cross peak has a negative slope confirming that the passive couplings JAX and JBX are of the same sign. In conclusion, the geminal and vicinal coupling constants are of opposite sign.1. C. Griesinger, O.W. Sorensen & R.R. Ernst, J. Magn. Reson. 75, ; 474 - 492 (1987).
2. The ecosygpph pulse program produces spectra similar to those described in reference 1 as "complimentary" E.COSY spectra. The slope of the lines through the cross peaks in "complementary" E.COSY spectra are of opposite sign to those obtained from the E.COSY spectra described in reference 1.
20 comments:
Interesting, but what information does the sign of the coupling constant provide about the molecule?
Hi John,
Thank you for your comment and question. The sign of the coupling constant can indeed provide information about a molecule. It is known ,for example that three-bond vicinal proton coupling constants are positive whereas two-bond geminal proton coupling constants are negative. If one was trying to identify an unknown sample and found that a particular coupling constant was negative then one might have reason to believe that the protons were geminal to one another rather than vicinal.
Glenn
What is active and passive coupling???I searched but didn't find a good definition.
Bhaswati,
In the COSY spectrum, the active coupling is the coupling giving rise to the COSY cross peak being considered and the passive coupling is not. For a example in an ABX spin system, if one is considering the cross peaks between A and B then the active coupling is JAB and the passive couplings are JAX and JBX.
Glenn
Hi! Can we use gDQFCOSY (from Varian pulse sequence library) for the same purpose?
Anonymous,
I do not know the answer to your question.
Glenn
can you specify the experimental parameters for ecosygpph bruker pulse program .. i am not able to reproduce the spectra using PHE in D2O..
regards,
rajesh
Rajesh,
Pl1 = 0
pl10 = 9.63
p1 = 11.88u
p2 = 23.76u
p16 = 1000u
p17 = 2500u
nd0 = 1
ns = 4
ds = 16
td0 = 2k
td1 = 256
Fnmode = TPPI
gpz1 = 40 %
gpnam1 = SINE.100
Glenn
Thanks Glenn, it's very helpful. Do you know if there's a way to assign spins A and B stereospecifically for a similar molecule?
Anonymous,
I don't think this E-COSY experiment will allow you to make such an assignment. I would suggest a NOESY measurement if there are enough protons in the system.
Glenn
Hello sir,E.COSY is applied for strong coupling also..or not
Dear AJAY,
Thank you for your question. Although I have not looked into the matter in any depth, I suspect the ECOSY method can be used to measure the relative signs of coupling constants for strongly coupled spins - at least to a point. If the coupling is much larger than the chemical shift difference then I suspect the analysis would be non-trivial.
Glenn
Hello sir, I am working with a molecule having five coupled nuclei (four 19F and one 1H). Do you think I can use E.COSY to find out the relative signs of only 19F nuclei while 1H is decoupled during acquisition?
Thanks,
Amanddep.
AMAN,
I think you should be able to use this method to determine relative signs of 19F-19F coupling constants however I think you will have to use 1H decoupling for the entire sequence (except the recycyle delay).
Glenn
Dear Glenn Facey!
We recorded E-COSY spectra of a compound on Jeol-600 MHZ using default pulse sequence (ecosy_phase.jxp).
My purpose is to calculate J-values to fix the stereochemistry of compound, but, in the spectra all the signals (Off-diagonal peaks) are simmetrical with same J value for all protons. Could you please suggest me if any parameters below to be corrected.
Details:
x_domainn : Proton
x_offset : 5[ppm]
x_sweep :15[ppm]
x_points : 1024
x_prescans : 4
mod_return : 1
y_points : 256
x_acq_time : 0.11375[s]
x_resolution : 8.79159[Hz]
y_acq_time : 28.43628[ms]
y_resolution :35.16635[Hz]
Y.K. Nalli,
I am not familiar with the JEOL software or parameters so not in a position to offer advice. I suggest that you contact one of the JEOL application chemists. They are very knowledgeable.
Glenn
Hi Glenn,
I completed PhD in solid state NMR with Dr PK Madhu, TIFR, Mumbai, India in 2009.
I was working with YK Nalli to obtain ECosy spectra of phenylalanine. After optimising parameters with jeol engineers we got a reasonable spectra but all the slopes are of one sign. We used L-phenylalanine as sample.
Do you think using D-phenylalanine can help? Should be try L-phenylalanine.HCl as a sample.
I can run the same experiment on a Bruker spectrometer.
Please let me know if there is another trick I am missing.
Rajendra,
I do not know why the slopes are all the same. I don't think it has anything to do with which optical isomer of Phenylalanine used.
Glenn
Hellow Sir. Can you specify the processing parameters for ecosygpph pulse program? "edp" parameter
Anonymous,
These data were processed with QSIN = 2 apodization.
Glenn
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