Coupling constant, determination

The coupling interaction between directly bonded N—H is generally dominated by the Fermi contact term, as evidenced by the dependence of 7( N—H) on the amount of s character in the bond. Table 15 lists some illustrative N—H coupling constants, determined under comparable solvent conditions, as a function of the s character in the bonding orbitals. 

The relative content of the three kinds of dyad in a polymer sample can be determined by measuring the peak area ratios of the three kinds of quartets in the H-NMR spectrum taken at 100 MHz in benzene-d6 solution at 70° C. Accuracy of the analysis could be raised to +1-2% by using the data of chemical shifts and coupling constants determined at 220 MHz. Thus, the microstructure analysis by H-NMR spectrum can be used for routine work, because propylene oxide-a-d can be prepared easily. 

The chemical shifts and the 29Si-29Si coupling constants (determined from the ID-INADEQUATE spectra) are summarized in Table 1. Figure 1 shows the ID-INADEQUATE spectrum of 4. If all the 29Si-29Si couplings can be determined, the structure of the compound can be easily derived. 

The /i-13C-labelled naphthalenes obtained have been characterized by their 13C-NMR chemical shifts and 13C-13C coupling constants determined in CD3OD. 

P and 195Pt shifts and signs of e coupling constants determined... 

The value of P—H coupling constant determined from the spectrum is slightly different from the true value of V(P H) because of second-order effects (see later) and, hence, is designated as the apparent P - H coupling constant, iJ (P—H). 

It is worth mentioning that the relative populations of linear and cyclic structures can be shifted by temperature. A recent work which couples experimental measurements with ab initio calculations of quadupole coupling constants determined that rings of six formamide molecules dominate in the liquid state at low temperatures, but are replaced by linear tetramers as T approaches 400° K. 

The coupling constants determined are shown at the side of formula 207. It may be seen that large, diaxial, space couplings of 10—11 Hz appear between H-2 and H-3, H-3 and H-4, and H-4 and H-5a this is only possible if 207 assumes the Cl (d) conformation, which is the... 

Table 1 Comparison of170 and D quadrupole coupling constants determined in simulations with the experimental values...

The NMR data accumulated fix the calystegines identified to date is quite comprehensive and should enable novel structures in the class to be elucidated fairly easily by comparison with established structures. The H and I3C NMR chemical shifts and coupling constants determined for the above nine alkaloids are tabulated in Table 1 and Table 2, respectively. 

However, because of the difficulty in measuring the correlation time, the quadrupole coupling constant determined from in the liquid state is not always reliable even when 17 is truly negligible. In special instances, r can be determined from Raman line shapes26 or the 7g of another quadrupole nucleus in the same molecule whose nuclear quadrupole coupling constant is accurately known.24... 

Paramagnetic complexes of semiquinones with Tl" (81), have been prepared by the reaction of Et2TlCl with the sodium salt of the o-semiquinones. Their e.s.r. spectra were reported, and hyperfine coupling constants determined. ... 

Table 8.2. Chemical shifts and coupling constants determined by 31P- and 19F-NMR for species existing in the system l,6-anhydro-2,3,4-tri-0-benzyl-f -D-glucopyranose-PF5 29)...

Some coupling constants (determined by direct observation of the n.m.r. spectra... 

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