Like a COSY experiment, an HMBC dataset offers many combinations of atom connectivity. The goal for the elucidator is to assess each correlation and narrow down a set of fragments that support the data.
For every correlation in a 1H-13C HMBC spectrum, an elucidator must decide whether a correlation corresponds to a 2J, 3J or 4J coupling (NOTE: this is dependent on what the coupling constant is set to in the HMBC sequence). Below is a structural list for all H to C connections—heteroatoms are not shown in the list for the sake of simplicity. The 2J coupling, outlined with a blue box, the 3J coupling, outlined in a green box, and the 4J coupling, outlined with a purple box, offers 3, 6 and 14 possible combinations, respectively.