Signal multiplicity

Population transfer experiments may be selective or nonselective. Selective population transfer experiments have found only limited use for signal multiplicity assignments (SSrensen et al, 1974) or for determining signs of coupling constants (Chalmers et al., 1974 Pachler and Wessels, 1973), since this is better done by employing distortionless enhancement by polarization transfer (DEPT) or Correlated Spectroscopy (COSY) experiments. However, nonselective population transfer experiments, such as INEPT or DEPT (presented later) have found wide application. 

Determination of the elemental composition should be started with the M + 2 peak. Chlorine, bromine, sulfur, and silicone are easily detected due to characteristic signal multiplicity for each of these elements. There is a simple mle to check the presence of the main A + 2 elements. If the intensity of the M + 2 peak constitutes less than 3% of the intensity of the M peak, the compound does not contain chlorine, bromine, sulfur, or silicon atoms. This rule is valid for the fragment ions as well, while its applicability is confirmed by the data summarized in Table 5.4. 

Because the nucleus is isotopically rare, it is extremely unlikely that any two adjacent carbon atoms in a molecule will both be As a consequence, coupling is not observed in NMR spectra i.e. there is no signal multiplicity or splitting in a NMR spectrum due coupling. couples strongly to any... 

Sophorine was isolated from Sophora alopecuroides (26). The nature of MS decay showed that sophorine is a quinolizidine alkaloid of the lupinine type. The IR spectrum suggests the presence of a franj-quinolizidine moiety (2675-2945 cm ) and an — NH—CO— group (1605 and 1683 cm ). On the basis of chemical shift analysis and signal multiplicity of H- and C-NMR spectra as well as biosynthetic considerations, structure 59 was proposed for sophorine. 

As can be seen in Table 3.1 for commonly used deuterated solvents, deviations of Jcu/Jcd from the ratio yH/yD are rare and small, so that only J(H or JCD need be determined experimentally. To conclude, all relations found for JCH can also be derived for JCD. The signal multiplicities, however, are different (3 for CD, 5 for CD2 and 7 for CD3, respectively) because of different spin quantum numbers (/D = 1 /H = ). 

Table 3.26 Changes in signal multiplicity for diastereotopic and nondiastereotopic ligands...

The 13C signal multiplicities were determined by DEPT experiments and shown in Fig. 8.8. 

Both were recorded over 5000 Hz range in deuterated dimethylsulphoxide on FT-80 A-80 MHz NMR spectrometer using tetramethylsilane as reference standard. The carbon chemical shift value are assigned on the basis of signal multiplicity, chemical shits and the comparison with the chemical shits of model compounds. 

The structure of the complexes can be gleaned from the NMR spectra of L, 1 1 and 1 2 Lai complexes as shown in Fig. 4.3. It is to be noted that LaL2 and hydrated LaL species give the same signal multiplicity indicating C4 symmetry of L. This is not the same for the anhydrous [LaL]3+ complex in so far as the CH2P(0)t protons, Hp are concerned. 

Figure 12.16. DEPT signal intensity as a function of signal multiplicity and the tip angle of variable pulse 0.

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