Everyone should be familiar with the HMBC or Heteronuclear Multiple Bond Correlation (HMBC) experiment. The HMBC provides ¹H – ¹³C correlations over two, three or four bonds and is an extremely useful experiment in the toolbox for structural determination. The one bond Heteronuclear Single Quantum Coherence (HSQC) experiment, ¹J ¹H-¹³C and the Correlation Spectroscopy (COSY), ³J ¹H-¹H experiment make up the standard complement of experiments used when trying to solve an unknown structure by NMR.

Another experiment that should be added to the mix is the The Heteronuclear 2 Bond Correlation experiment (H2BC)¹. As the name suggests the H2BC only observes two bond correlations. It achieves this by using the ³J ¹H-¹H COSY interaction combined with ¹J ¹H-¹³C HMQC (Heteronuclear Multiple Quantum Coherence). The net result is that the all two bond interactions are observed while excluding the longer range interactions. On the positive side of the ledger this experiment is much more sensitive that the HMBC saving time and expense. On the negative side, two bond correlations to carbons that lack hydrogen atoms will not be observed as they do not have a COSY interaction that allows the H2BC to work.

For a more complete explanation of the H2BC experiment go to the excellent NMR Blog by Glenn Facey https://u-of-o-nmr-facility.blogspot.com.au/

1. Nyberg, Duus, Sorensen.  J. Am. Chem. Soc. 127, 6154 (2005).