JOURNAL OF MAGNETIC RESONANCE 86,199-203 ( 1990) Extracting Subspectra from Overlapping Regions. DOUBLE TOCSY

The TOCSY-HOHAHA experiment (I, 2) provides an efficient way to achieve mu ltiple-relayed coherence transfer in high-resolution NMR. By this method, sub-spectra can be extracted from overcrowded regions, thereby allowing measurements of chemical shifts and coupling constants. Subspectra can be obtained either from the 2D experiment by taking cross sections or directly from the ID version (3-5). The sensitivity is not, in practice, significantly different in the two cases, since the relaxation during the selective pulse of the 1D experiment is essentially replaced by the relaxation during the t, evolution period of the 2D experiment. However, the z-filtering technique (6-8) for correcting phase and intensity distortions is more easily implemented in the ID version, since it usually requires too long a measur ing time in the 2D scheme. Even so, a significant degree of strong coupling in the spin system can spoil the fidelity of subspectra reproduction, making the measurement of NMR parameters more difficult. Unfortunately, there does not seem to be a satisfactory solution to this problem. To date, the most efficient m ixing schemes have been based on decoupl ing se