Dihedral angle method

The percent displacement from the ideal TBP toward the RP is calculated from unit bond distances on the basis of the dihedral angle method using sulfur as the pivotal ligand. 

The silicon atom in the crystal of cationic complex [Ph3Si(bipy)] I is pentacoordinated but the bond lengths are not determined Geometrical distortion from the TBP to the SPY configuration expresses from the sum of dihedral angle method desaibed in Refs. Two crystallo-... 

Although the dihedral angle method has helped to resolve the complexes more clearly into different conformers, there are nonetheless problems associated with it for example, for intermediate geometries there is some arbitrariness in relating angles in observed structures to corresponding angles in the reference conformers. Moreover, the method requires an a priori definition of what constitutes a SQP, so that the i5,y(SQP) s may be calculated. 

According to the namre of the empirical potential energy function, described in Chapter 2, different motions can take place on different time scales, e.g., bond stretching and bond angle bending vs. dihedral angle librations and non-bond interactions. Multiple time step (MTS) methods [38-40,42] allow one to use different integration time steps in the same simulation so as to treat the time development of the slow and fast movements most effectively. 

The second separation method involves n.O.e. experiments in combination with non-selective relaxation-rate measurements. One example concerns the orientation of the anomeric hydroxyl group of molecule 2 in Me2SO solution. By measuring nonselective spin-lattice relaxation-rat s and n.0.e. values for OH-1, H-1, H-2, H-3, and H-4, and solving the system of Eq. 13, the various py values were calculated. Using these and the correlation time, t, obtained by C relaxation measurements, the various interproton distances were calculated. The distances between the ring protons of 2, as well as the computer-simulated values for the H-l,OH and H-2,OH distances was commensurate with a dihedral angle of 60 30° for the H-l-C-l-OH array, as had also been deduced by the deuterium-substitution method mentioned earlier. 

Calculated using r2,3 = 1.80 A, this being the value obtained by both methods of calculation. Input parameters bond lengths, C-H 1.10 and C-C 1.54 A bond angles 109.5°, dihedral angles, 0° and 120°. From Refs. 87 and 88. 

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