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Thursday, January 3, 2008

Searching for Small Peaks in 1H Spectra - 13C Decoupling

It is not usually necessary to decouple 13C while observing protons as 13C is only 1.1% naturally abundant and 12C has no spin. The only thing 13C decoupling will do for you is collapse the very small 13C satellites into single resonances which (aside from a very small isotope effect) will be coincident with the proton resonances for the protons bonded to 12C. In certain instances however, 13C decoupling is desirable. Such is the case when one is looking for very small peaks in a 1H spectrum. Below is an example of how such small peaks can be observed more easily when the 13C satellites are removed with decoupling. The lower trace is a conventional proton spectrum while the upper trace is the same spectrum with 13C decoupling. This is very useful if one is searching for small amounts of impurities underneath the 13C satellites of much larger resonances.


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