I am characterizing one complicated 13C NMR, which has more CH-, CH2-, and CH3- signals in the aliphatic region. I heard Inverse-Gated (IG) 13C NMR will give good information regarding this case. What is the actual difference from normal 13C NMR? From google I come to know that it will give carbon multiplicity by coupling with adjacent proton. Also it will give well separated high intensity for all (CH-, CH2-, and CH3-) irrespective of concentration. Is it true or not honestly I don’t have idea. Please give me some valuable information and clarification regarding this.
Thank you in advance!
Normally during a solution-state 13C NMR experiment, the 1H decoupling is on during the entire duration of the experiment (recycle delay+expt time+acquisition time). However, this can lead to Nuclear Overhauser effect (NOE), which will enhance the signals from certain carbons disproportionately, leading to non-quantitative spectra. With inverse gated decoupling, the decoupling is on only during the acquisition period, which minimizes NOE enhancements, and more quantitative results.
Use inverse gated decoupling when quantitative results are desired. Otherwise not required. It has nothing to do with multiplicity.
Glenn Facey's blog has good explanations for this stuff: http://u-of-o-nmr-facility.blogspot.ca/2008/05/modes-of-heteronuclear-broadband.html
Dear Dr Majumdar,
Many thanks for your valuable link.
So because of less NOE we can integrate the 13C signal and from that value we can under stand the abundance of particular signal (like CH-, CH2- and CH3)?
kind regards,
S. Pappuru
Dear Sreenath,
In short, IG-13CNMR will give you the possibility of "trusting" the integral values of the peaks (which normally is not possible with standard 13CNMR). So yes, you will be able to see how many C atoms contribute to each peak like for 1HNMR.
Yes, you should be able to integrate the IG 13C spectrum. But there is no absolute guarantee it will be perfect. Also, if the sample is not 13C labelled, paramagnetic relaxation agents are sometimes used to ensure complete return to equilibrium, which will help with more accurate quantitation.
Dear Silvio Curia and Dr. Rudraksha Dutta Majumdar,
Thank you so much.
With inverse gated time to collect an NMR spectra are reduced and signal intensity is enhanced.
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