Vicinal coupling constant

Figure 13 20 there are two other vinylic protons Assuming that the coupling constant between the two geminal protons in ArCH=CH2 is 2 Hz and the vicinal coupling constants are 12 Hz (cis) and 16 Hz (trans) describe the splitting pattern for each of these other two vinylic hydrogens... 

Vicinal coupling constants Jhh indicate very clearly the relative configuration of the coupling protons. Their contribution depends, according to the Karplus-Conroy equation... 

It is now generally realized that the angular dependence of vicinal coupling constants is considerably mare complex than was at first appreciated (24, 38, 39) and that care must be exercised in utilizing... 

In view of the possible ambiguities which can attend conformational assignments based on vicinal coupling constants, it is fortunate that both long-range and geminal couplings each exhibit stereospecific dependences. 

Some high vicinal coupling constants have been reported for vinyl systems. The trans PC=CH coupling constants for (68, Y = NMca) and (68, Y = Cl) are 57.0 and 77.6 Hz respectively. This is well above the usual range (28—51 Hz). The cis PC=CH coupling constants of (68,... 

It is difficult to decide whether the discrepancy between the calculated and experimental data is due to a different conformational preference of the thietane dioxides in the liquid and the solid phase, or to the crude approximations included in the Karplus-Barfield equation. However, the relationship between vicinal coupling constants and dihedral angles appears qualitatively valid in thietane oxides and dioxides, particularly if trends instead of exact values are discussed . At any rate thietane dioxides, 1,3-dithietane dioxides and tetroxides maintain either planarity or a slightly distorted average vibrating conformation with a low barrier to ring planarity . 

TABLE 2.5. Vicinal Coupling Constants as a Function of Multiple Electronegative Substituents... 

Vicinal coupling constants between fluorine and hydrogen are generally between 18-20 Hz for both primary and secondary CF2 groups. On the other hand, H—H coupling constants between vicinal hydrogens are much smaller in these compounds, between 4 and 8 Hz. 

Corsaro and co-workers studied the reaction of pyridazine, pyrimidine, and pyrazine with benzonitrile oxide and utilized H NMR spectral analysis to determine the exact structure of all the cyclized products obtained from these reactions <1996T6421>, the results of which are outlined in Table 1. The structure of the bis-adduct product 21 of reaction of pyridazine with benzonitrile oxide was determined from the chemical shifts of the 4- and 5-isoxazolinic protons at 3.76 and 4.78 ppm and coupled with the azomethine H at 6.85 ppm and with the 5-oxadiazolinic H at 5.07 ppm, respectively. They determined that the bis-adduct possessed /(-stereochemistry as a result of the large vicinal coupling constant (9.1 Hz). Similarly, the relative stereochemistry of the bis-adducts of the pyrimidine products 22-25 and pyrazine products 26, 27 was determined from the vicinal coupling constants. 

Adiwidaja, G., Meyer, B., and Thiem, ]., Synthesis and crystal structure of endo-2-dimethylphosphono-exo-2-hydroxy-(-)camphene for the determination of 3J(CCCP) vicinal coupling constants, Z. Naturforsch. Teil B, 34B, 1547, 1979. 

Fig. 10.18. IDR (Inverted Direct Response)—HSQC-TOCSY pulse sequence. The experiment first uses an HSQC sequence to label protons with the chemical shift of their directly bound carbons, followed by an isotropic mixing period that propagates magnetization to vicinal neighbor and more distant protons. The extent to which magnetization is propagated in the experiment is a function of both the size of the intervening vicinal coupling constants and the duration of the mixing period. After isotropic mixing, direct responses are inverted by the experiment and proton detection begins.

A new NMR method for the determination of the anomeric configuration in mono- and disaccharides has been described.18 The protocol is based on the different cross-correlated relaxation between proton chemical shift anisotropy (CSA) and dipolar relaxation for the a and (3 anomers of sugars. Only the ot-anomers show the presence of CSA (HI or Hl )-proton dipole (H1-H2 or Hl -H2 ) in the longitudinal relaxation of the anomeric protons. The method is of special interest for cases in which vicinal coupling constants between HI and H2 in both anomers a and (3 are similar and small, such as D-mannose, and the non-ambiguous description of the anomeric configuration needs additional measurements. 

P. W. Kent, R. A. Dwek, and N. F. Taylor, Tetrahedron, 27 (1971) 3887-3891. Subsequent determinations for additional fluorinated pyranoses showed that Vo values are not always larger than values as described in this Section, the values of gauche-vicinal coupling-constants have been shown to depend on a number of complex factors. 

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