Interrupted-decoupling experiment

Interrupted-decoupling experiments provide the spectra required for the analytical procedures described in the following two sections. 

Fig. 8.23. An example of the interrupted-decoupling experiment for suppression of the protonated carbon resonances is shown. The labeled peaks correspond to the labeled carbons in the structure. (Reproduced from Ref. [76], 1984 C. Shields.)...

Interrupted-Proton-Decoupling Experiments. Interrupted-pro-ton-decoupling experiments were carried out with a 50- xs interruption. This technique selects quaternary carbons (those lacking an attached proton) and rapidly moving methyl carbons. Resonances from methylene and methine carbons are suppressed unless, for some reason, their motion within the solid occurs at a rate similar to that of methyl groups. In essence, the interrupted-proton-decoupling experiment, which has not been previously reported for amber samples, provides an alternative fingerprint for the samples. 

An experiment that is useful for assigning nonprotonated carbon resonances in the NMR spectrum is the interrupted-decoupling CP experiment [74,75]. In this experiment, the decoupling of the protons is interrupted (by turning off the proton rf field) for a predetermined time. During the interrupted-decoupling period, 3C... 

The zero sum of intensities in a multiplet in these differential polarization transfer experiments means that any decoupling that causes all the lines to coalesce results in exact cancellation of intensities. Several methods have been devised to avoid this problem when decoupling is required. One is pulse-interrupted precession,which results in a net polarization transfer, as does the insertion of a properly chosen delay period in the INEPT sequence (as in Figure 12) so that all members of a multiplet appear positively enhanced, i.e., INEPT with refocusing (INEPTR). The DEPT (Distortionless Enhancement Polarization Transfer) sequence gives undistorted relative intensities of the multiplet components. 

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