Coupling constant value

Two isomeric structures can be obtained for these products ( -113 and/or Z-113). The stereochemistry was conveniently elucidated on the basis of NMR data which showed coupling constant values 7(H,CO) consistent with the -isomers only. The formation of 113 was explained to occur via the enolate salts (86JHC199). Catalytic... 

A P,C correlation experiment also requires that we use a predefined coupling constant value to determine the mixing time. A brief look at the proton decoupled carbon-13 spectrum (Fig.14) shows that is very large (around 200 Hz), while the long-range JPC values are much smaller (around 5-10 Hz). 

Thus tin chemical shifts are of considerable use in structural studies. In addition, tin-element coupling constants are easily visible, and particularly in proton and carbon-13 spectra the relevant coupling constant values are of diagnostic use for example both tin-proton and tin-carbon coupling constants show a Karplus-type behaviour. 

Lead-proton and lead-carbon coupling constant values have structural uses, as with tin. Lead chemical shifts are quite sensitive to temperature variations. 

The information and examples presented in this chapter should enable the reader to predict chemical shift and coupling constant values for a single fluorine substituent in virtually any possible environment in which it might be encountered. 

TABLE 1 Optimal duration of the t, delays for maximal Vch suppression as a function of the minimum (VcHmin) and maximum (VcHmax) coupling constant values... 

The limits of the original BIRD-FIMBC sequence and the excellent /ci 1 filter quality of the double tuned G-BIRD element is exemplified in the spectra obtained with the molecule 1,3-butadiynyl (ferf-butyl) diphenyl-silane (Figure 6). This molecule provides a stringent test, since it contains all together aliphatic, aromatic and acetylenic protons, and the corresponding ch coupling constant values vary from 125 to 260 Flz. 

Table 24. Free-ion spin-orbit coupling constant values ...

Hie coupling constants values of H-16 allowed the determination of the configuration at C-16. In 189, H-16 must be axially oriented, antiperiplanar with axial H-17, because one of the coupling constants is 9.5 Hz. On the other hand, H-16 in 190 must be equatorially oriented. The different configuration at C-16 deeply influences the chemical shift of H-15a, which is strongly shielded in 189 with respect to 190 (0.37 ppm versus 1.13 ppm). 

The employment of NMR-active isotopes permits to access experimental parameters which are intrinsically difficult to measure, unless a significant concentration of the sugar is present in the NMR tube. For instance, aqueous solutions of N-acetyIncuraminic acid, labeled with 13C at Cl, C2, and/or C3, were analyzed to detect and quantify the various chemical species present in equilibrium at different pHs. In fact, in addition to the expected a and (3 pyranose forms, acyclic keto, keto hydrate and enol forms were identified on the basis of 13C NMR spectroscopic data. Besides, DFT methods were employed to predict the effect of enol and hydrate structure on the coupling constant values Jc,u and /c c involving C2 and C3, finding that 2/c2,h3 can be safely used to differentiate the cis and tram isomers of the enol forms.9... 

Hoye, T. R. Zhao, H. Method for Easily Determining Coupling Constant Values An Addendum to A Practical Guide to First-Order Multiplet Analysis in H NMR Spectroscopy . J. Org. Chem. 2002, 67, 4014-4016. 

The extensive delocalization and aromatic character of pyridones, pyrones, etc. are shown by their chemical shift and coupling constant values (Table 8). By contrast, pyrans and thiins show chemical shifts characteristic of alkenic systems (Table 9). For these and for rings containing only a single endocyclic bond (Table 10), H NMR spectroscopy offers a most useful tool for structure determination. 

The following table gives the most important fluorine coupling constants, namely, JFN, JFCF, and JCF, together with some typical examples.1-9 The coupling constant values vary with the solvent used.3 The book by Emsley et al.1 gives a complete, detailed list of various compounds. 

Snider and Duvall published the first geminal coupling constant in the case of the 1,2-oxazetidine carboxylate derivative 28a (Table 1 Figure 9) and confirmed the formation of the four-membered ring by means of heteronuclear multiple bond correlations (HMBC) (Table 1) <2003TL3067>. Vicinal coupling constant values 37h-h are now available in the... 

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