HMBC spectra are designed to show correlations between hydrogens and heteronuclei separated by two or more bonds, however, single bond correlations are often present in HMBC spectra as well. Like the multiple bond correlations in HSQC spectra discussed in the previous post, single bond correlations in HMBC spectra can be confusing if you are not expecting them, but once aware that they may be present they are fairly easy to identify.
