Vicinal coupling, dependence

The most well-known stereoelectronic analysis of the vicinal coupling dependence from the respective dihedral AXYB angle is exemplified by the famous equation suggested by Karplus. ... 

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. 

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. 

Particularly startling is the 0.77 Hz change observed for the cis H—F coupling constant of tram-1,2-difluoroethylene. This compound does not have any net dipole moment and the geminal H—F coupling does not display any appreciable solvent dependence, yet the vicinal coupling involving the same nuclei is solvent dependent. 

Vicinal Coupling, V ( H, F). The signs of vicinal couplings were found to be absolutely positive, and their angular dependence parallels" that of proton-proton coupling-constants, - ranging between 0 and... 

The vicinal coupling (protons on adjacent carbon atoms) h-c-c-h have values 0 - 16 Hz depending mainly on the dihedral angle (f). 

The so-called Karplus relationship expresses approximately, the angular dependence of the vicinal coupling constant as ... 

Analogous Karplus-type angular dependences are observed for vicinal couplings of other... 

Conformational characteristics of DME in the gas phase are studied by the NMR method. Observed H- H and 13C-1H NMR vicinal coupling constants are compared with those determined in nonpolar solvents. The values observed in the gas phase and in solution do not exhibit any appreciable discontinuity at the transition. RIS simulations of these vicinal coupling constants yield conformational energies given above. In these treatments, the neighbor-dependent character of the bond rotation is rigorously taken into account. 

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