Getting the Most Out of HSQC and HMBC Spectra
Abstract As the title suggests, this chapter focuses on HSQC and HMBC spectra, two critically important spectra for organic structure determination by two-dimensional NMR. The relative merits of the HSQC sequence and the alternative HMQC sequence are discussed, and the performances of different versions of the HSQC sequence are evaluated, using three test compounds. It is shown that recent modifications of the HSQC sequence have eliminated or minimized earlier weaknesses of this sequence, leading to a more than twofold increase in signal/noise, particularly for edited HSQC spectra. In the case of HMBC, the impact of recent modifications of the sequence is much less than for HSQC. However, the choice of acquisition and processing parameters can have a dramatic effect on the signal/noise of HMBC spectra. A few of the numerous variants of HMBC that have been proposed to compensate for weaknesses of this sequence are considered. While they potentially yield more information, this is at the expense of signal/noise.