The advantages of the indirect detection
The reverse detection technique became increasingly popular due to the software improvements of the spectrometers from one hand and to the increase of the sensitivity of the detection of a X nucleus by the indirect way. In fact the reverse detection solves the problem of the low concentrations. Moreover, it allows to reach the NMR parameters such as chemical shits, coupling constants and relaxation time spin lattice for nuclei impossible to study by the direct detection. (Fig. 28)
For example it is not always obvious to get NMR spectra for nuclei such as
,
,
and sometimes even
in direct observation.
Consequently, the reverse detection becomes the only possible way either for
correlation in the case of peptides or proteins or also for
correlation in the case of organometallic compounds.
In each of these examples the reverse detection allowed to determine the chemical shift of the heteronucleus together with the coupling constants .J(X-H).
The arrows figure the magnetization transfer from the proton towards the
and then from the
towards the proton.
