Abstract
The heteronuclear multiple bond correlation (HMBC) pulse sequence provides a powerful tool for determining structures of unknown organic compounds. However, it is also the least sensitive of the basic two-dimensional (2-D) nuclear magnetic resonance (NMR) sequences used for this purpose. Here, the basic sequence is described, followed by a discussion of how the sensitivity and information content of HMBC spectra can be improved by appropriate parameter choices. In addition, possible ambiguities in interpreting HMBC spectra are pointed out and discussed. Modified versions of the standard (gradient-selected) HMBC sequences are also briefly mentioned. Finally, it is pointed out that, while the gradient-selected HMBC sequence will normally be the sequence of choice, there are specific circumstances where use of the earlier phase-cycled HMBC sequences or even the earlier, lower sensitivity 13C-detected analogs of HMBC may actually give better results.
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