Coupling constant dihedral angle dependence

Eq. (8.7), which provides the scalar coupling constant due to the interaction between nuclei, is analogous to Eq. (2.29), used to describe the dihedral angle dependence of the contact coupling constant due to the interaction between nuclei and electrons. 

Fig. 10. 3D plot and contour map for Vhccch in propane, calculated as a function of the dihedral angles ip, and ip3 by DFT/FPT at 30° intervals of the angles. 3D spline interpolations were used to create the graphs, which illustrate how the coupling constant changes sign, depending on the values of, i and, ... 

Couper, Archibald S., 3 Coupling constant (J), 503, 506, 507-508 dihedral angle dependence, 544 Covalent bond, 12-14, 44 Cracking, in petroleum refining, 70 Crafts, James M., 451 m-Cresol, 939 acidity of, 944... 

Extension of this type of analysis to scalar coupling Interactions Involving other nuclei requires establishment of the dihedral angle dependence of the vicinal couplings. Three approaches have been used (1) Measurement of coupling constants In conformatlonally constrained molecules (2) correlation of observed couplings with rotamer distributions In flexible molecules deduced previously on the basis of values (3)... 

Figure 12.82 Dihedral angle dependence of j, and in typical acyclic systems. Narrower ranges of the coupling constant values can be defined for specific patters (e.g. 1,2-dioxygenated systems).

N. Juranic, E. Atanasova, M.C. Moncrieffe, F.G. Prendergast, S. Macura, Calciumbinding proteins afford calibration of dihedral-angle dependence of Jnct coupling constant in aspartate and asparagine residues, J. Magn. Reson. 175 (2005) 222. 

The vicinal coupling constants are mainly dependent on the dihedral angle 4> ... 

Krivdin and co-workers ° applied a double perturbation theory (DPT) at the second order level of approximation formalism to examine the dihedral angle dependence of the Fermi-contact (FC) contribution to nuclear spin-spin coupling constants. The authors have derived an analytical expression relating the FC term of /(H,H) across the aliphatic single carbon-carbon bond to the dihedral angle describing inner rotation around the C-C bond in the ten-electron ten-orbital moiety H-C-C-H. In particular, the authors have shown that extrema of H,H) are observed at q> = nn [n = 0, 1, 2,...), which provides a theore-... 

From a comparison of proton-fluorine coupling constants and bond angles in a series of cyclic organic molecules, it has been found that V( H, F) generally decreases as the H-C-C-F bond angle increases. In addition, the dihedral angle dependence of V( H, F) is very similar to the dependence of V( H, H), i.e. ( H, F) has a maximum value when the dihedral angle 0 between H and F is 0° and 180°,... 

Representative values for Vpx coupling constants through intervening C, N, O, or other heteroatoms are presented in Table V. As might be expected from the dihedral-angle dependence of vicinal Vhcch coupling constants,... 

J is almost always positive and its magnitude often exceeds that of T. It always depends in a predictable way on the dihedral angle ( ) between the outer two of the tluee bonds in die coupling patliway. Karplus first showed theoretically that T varies to a good approximation as A cos ( ) + B cos ( ), where A and B are constants, and also that A S>B [17]. Flis equation has received wide-ranging... 

Vicinal CH coupling constants Hqh resemble vicinal HH coupling constants in the way that they depend on the cosine of the dihedral angle 9 between the CC bond to the coupled C atom and the C//bond to the coupled proton (cf Fig. 2.16), as illustrated by the Newman projections of the conformers 20a-c of a propane fragment. 

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