Part C. Two-Dimensional Techniques The Experiments

There are many ways to approach the acquisition, processing, display, and even interpretation of 2D NMR experiments. The sections that follow describe many of the 2D experiments that have been discussed thus far and provide guidelines for their performance using the States method of detection. For the best results, 2D experiments should be performed at constant temperature (ideally, just above room temperature, in order to minimize evaporation of the solvent and degradation of the sample) and with a nonspinning sample. 

If computer speed and memory permit, 2D NMR experiments generally are planned so that at least a 2K (2,048-point) FT is carried out in each dimension. In this approach, np2 should be 1,024 and zero filled by one level, to 2,048, prior to the FT2. In addition, ni should then be linear predicted two- to fourfold, to 1,024, and zero filled by one level, to 2,048, before FTl. RT s of 0.8-1.2 s are generally sufficient, and most experiments call for the use of steady-state scans. 

There is, in fact, one disadvantage associated with acquiring a signal by means of gradients gradient versions of various 2D experiments exhibit a 2 / decrease in sensitivity with respect to their nongradient counterparts. This is, however, seldom a serious problem, especially with the proliferation of H-detected, 2D NMR experiments. 

A number of 2D spectra of the sesquiterpene natural product T-2 toxin (7-1) are collected in Part C to illustrate certain 2D experiments and the critical differences between them. 

7-7 Homonuclear Chemical-Shift Correlation Experiments Via Scalar Coupling 

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