Direct Heteronuclear Chemical-Shift Correlation Via Scalar Coupling

steady-state scans = 32, or 64 for long mixing times 

The ID version of this experiment is especially useful and is considered in Section 7-11. 

7-8 Direct Heteronuclear Chemical-Shift Correlation Via Scalar Coupling 

Heteronuclear chemical-shift correlation experiments usually involve protons as one of the nuclei and can be performed by detecting either protons or the X nuclei (the most common being C Section 6-2). The principal advantage of H-detected experiments is their sensitivity, which is a function of the gyromagnetic ratios (yh/Yx) - terms of the ratios of Larmor frequencies (instead of y s) at, say, 400 MHz for and 100 MHz for C, the benefit of detecting H rather than C is (400/100) / = 8. 

X-nucleus-detected experiments, however, have an advantage that can become important. In heteronuclear, chemical-shift correlation experiments, it is, as a rule, better to detect the nucleus with the more congested spectrum, which is almost always protons. On occasion, however, X-nucleus spectra are more crowded than their counterparts. In this situation, it could be better (if sensitivity permits) to carry out an experiment that detects the X nuclei. 

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