Measurement of the magnitude and the sign of small nJCH on protonated and non-protonated carbons

“A definitive NMR solution for the simple and accurate measurement of the magnitude and the sign of small heteronuclear coupling constants on protonated and non-protonated carbons”, by Josep Saurí, Juan Félix Espinosa and Teodor Parella; Angew. Chem. Int. Ed. (2012) DOI: 10.1002/anie.201108959

The measurement of long-range proton carbon coupling constants in natural-abundance molecules has always been a tranding topic for the NMR community. Despite the extensive number of NMR techniques that have been developed, there are still remain two unsolved problems pertaining to non-protonated carbons, namely, a) and accurate measurement of very small coupling constants (less than 2-3 Hz) , and b) the absence of a general and robust approach to determine the sign of the coupling. All these annoying drawbacks can be solved using the new selHSQMBC-TOCSY experiment. The method combines in a single pulse scheme all the benefits known for the widely used HSQMBC and HSQC-TOCSY experiments. Thus, the experiment is able to measuring the magnitude and the sign of ⁿJ_CH (n>1) with excellent accuracy and great simplicity by analyzing the relative sense of the displacement of IPAP multiplets in the direct dimension, showing particular interest to the application on quaternary carbons.