Values of coupling constants

The difficult problem of determining the relative amount of NH and OH tautomers in pyrazolin-5-ones has been solved using the value of coupling constants [83JPR(325)238]. 

The conformations and the axial and equatorial positions of the proton or group carrying a proton can be distinguished from the different values of coupling constants. 

I h. correct values of coupling constants were attributed to the appropriate protons by the analysis of antiphase structures of cross-peaks in DQF-COSY spectrum. 

TABLE 6.65 Spin-Spin Coupling (Hyperfine Splitting Constants) Values of coupling constant at given in gauss Involves protons unless otherwise indicated. 

Absolute values of coupling constants in Hz, 0.5 Hz, assumed to be positive. ... 

Absolute values of coupling constants, assumed to be positive239. 

Figure 13-28 shows typical values of coupling constants. The most commonly observed coupling constant is the 7-Hz splitting of protons on adjacent carbon atoms in freely rotating alkyl groups. 

It should be noted that single-transition INADEQUATE spectra are generally not suitable for the determination of coupling constants. This is because the readout of the couplings in F2 is affected by the isotope shifts. The combined use of F2 and F1 dimensions, which yields, in principle, the values of coupling constants, is problematic due to limited digital resolution in F A possible solution is to acquire two spectra with the selection of one transition at the time. This should still be a factor of V2 more sensitive compared to regular INADEQUATE on an equal time basis.5... 

As with organic compounds, the H and NMR spectra of organotins are used to assign protons and carbon atoms in addition, values of coupling constants " 7(" Sn- H) and "7(" Sn- C) are useful aids to bonding and to conformations. 

An extensive study by Coxon of the nuclear magnetic resonance spectra of thirty-six mediyl 4,6-O-benzylidene-a-D-aldohexopyrano-sides having the D-altro, D-manno, and D-gluco configurations included five p-toluenesulfonates. Values of coupling constants for these acetals supported the assignment of the C1(d) conformation to these pyranosides. 

Although we shall not work very much with the values of coupling constants, we should realize that, to an experienced person, they can often be the most important feature of an nmr spectrum the feature that gives exactly the kind of information about molecular structure that is being looked for. 

Tables 4-1 through 4-5 summarize values of coupling constants by class of structure, extracted from the references found at the end of the chapter. Further examples may be obtained by examining these references.

An unusually-large value of coupling constant, jpp, for a solid triphenylpho-... 

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