Coupling constants torsion angles

High-resolution n.m.r. spectroscopy of carbohydrates and glycoproteins has been reviewed.A new coupling-constant-torsion-angle relationship for three-bond spin-spin coupling has been derived. It is of the form of a Karplus... 

Figure 5 Schematic representation of a Cartesian dynamics protocol starting from random torsion angles. The weights for non bonded (i.e., van der Waals) interactions, unambiguous distance restraints, and ambiguous distance restraints are varied independently. The covalent interactions are maintained with full weight, co.aie - for the entire protocol. Weights for other experimental terms may be varied in an analogous way. Coupling constant restraints and anisotropy restraints are usually used only in a refinement stage.

For platinum(O) complexes, [42] analysis of the 1H chemical shifts and coupling constants as well as results of ID selective ROE experiments has allowed determination of the torsional angles j/ and

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Torsion Angle Constraints from Scalar Coupling Constants... 

Vicinal scalar coupling constants, 3J, between atoms separated by three covalent bonds from each other are related to the enclosed torsion angle, 6, by Karplus relations [45]. 

Most characteristic for the overall conformation of the cinchonan carbamates in solution is the dihedral angle of the torsion H8-C8-C9-H9, which can be inferred from the vicinal coupling constant of the NMR proton signal of H9. The experimentally measured coupling constant /hsh9 represents actually the average over the populations P(i) of the different conformers in solution according to [100]... 

Vicinal proton-carbon coupling constants in a series of conformationally rigid monosaccharide derivatives showed a satisfactory dependence of upon the torsion angles (2). The... 

A 5.5 Hz, B = -0.5 Hz and C = 0.8 Hz. This same dependence on torsion angle also justifies equation 4 and can be used for interpretation of experimental interglycosidic coupling constants in oligosaccharides. 

We think that the constancy of the n.O.e. values can be explained in this case by the averaging process during the NMR experiment (34). Since n.L.e. values and coupling constants depend in different, nonlinear ways on proton-proton distances and torsion angles, the time-averaged values of the geometrical parameters derived from n.O.e. values can differ from parsimeters indicated by coupling constants. 

Figure 7. A plot of the calculated FPT-INDO results for the one-bond coupling constant Jpr, in 2-methoxytetrahydropyran as a function of torsion angle around the aglycon C-0 bond with the methoxy group in axial (curve labeled with squares) and equatorial (stars) positions.

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