Bond and torsion angles

We also emphasize that the MD model does include the vibrational motions of bond, and torsional angles (in the minima of the respective potentials) but, somehow, these small scale fast motions are rapidly damped out in the melt, and do not affect the motion on the nanometer scale (and for corresponding times) significantly. 

The next step is to assume particular functional forms for the various terms. These can be extremely elaborate, but most are usually based on a simple, chemically intuitive model of the interactions, e.g. stretching of bonds, changes in bond and torsion angles, Coulomb forces and van der Waals intermolecular interactions. Thus, for a molecular solid comprised of discrete molecules, we might well use... 

TABLE 16. Selected structural parameters of die nitro group (bond lengths in A, bond and torsional angles in degrees, dipole moments in Debye) for the set of nitro compounds used in die parameterization of MM2 and MM3 as obtained by the two force fields and... 

Figure 2. Two maltotetraose models constructed from residues of glucose having different D. They have identical linkage bond and torsion angles.

Fig. 2. Endocyclic bond and torsional angles in heterocycles.33 (Within rings endocyclic bond angles. Outside rings torsional angles subtended by ring bonds.)...

Table 4.9. Interatomic distances R (in A), bond and torsional angles (degrees) for the lowest excited states of the Cs-symmetric Al(OH)4 model system calculated at the CASSCF level...

TABLE 31. Calculated and experimentally interatomic distances (A), bond and torsion angles (deg) of C(GeBr3)4a... 

An accumulation of methyl groups produces increasingly larger barriers (see Table 11). This shows clearly the effect of increasing rigidity, and suggests that in less crowded compounds it may be fairly easy to avoid contact by small distortions of bond and torsion angles. Similar effects are seen when there is a heteroatom or other substituent on one of... 

The reaction was carried out under mild conditions (hexane, —20 °C), and the product was purified by sublimation under reduced pressure. The yield of 76 was 89%, mp. 84°C. The structure was confirmed by H, °C, and B NMR spectra, by its mass spectrum and X-ray diffraction. The X-ray data show that the values of the bond and torsion angles indicating the molecule s viability are close to the calculated values (Figure 8) neglecting the difference between the substituents at the boron atom (H or z-Pr2N). The hetero ring and the naphthalene framework are virtually coplanar, and the r is also about 1.3. 

The molecules Se and Sio in Se-Sio exhibit the same molecular conformations as in the pure crystals of (D i) and of Sio D2). However, the molecular parameters of Se in Se-Sio show a slight variation of less than 1% of the mean values in the case of the bond and torsion angles and less than 0.1% in the case of the internuclear distances. As in pure Sio both enantiomorphic molecules are present in Ss-Sio in equal amounts. The site symmetry of Sio in Se-Sio is C2 as in pure Sio. However, the site symmetry of the Se molecules in Ss-Sio is reduced to C in comparison with Csi in pure S. The mean bond parameters of S and Sio are almost identical in Se-Sio compared to the pure components (Table 10). 

Another grouping of the various conformation search methods is based on the coordinate system in which they operate. For the potential advantages of the external (Cartesian) and internal (bond lengths, bond and torsional angles) systems, the reader is referred to Refs. 71 and 75. 

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