Valency angles distortion

The authors believe that the results are more readily explainable on the basis of a two-point absorption involving the vanadium-carbon-sulphur complex, the formation of which may be effected with little distortion of the tetrahedral valence angles. 

In many cases we can describe the situation by a schema (Fig. 4) showing the potential energy between the positions ( ) and (B ). The improbable conformation (c) is characterized by a distortion of the valence angles and repulsive forces acting on neighboring molecules. The calculations given in the appendix (i) are limited to one space component in the direction between the two possible conformations. 

Formation of a four-membered ring of carbon atoms can be achieved only with substantial distortion of the normal valence angles of carbon, regardless of whether the ring is planar or nonplanar. In cyclobutane, for example, if the valence bonds are assumed to lie along straight lines drawn between the carbon nuclei, each C-C-C bond angle will be 19.5° smaller than the 109.5° tetrahedral value ... 

The three carbon atoms of the cyclopropane ring lie in a plane. Therefore the angle strain is expected to be considerable because each C-C-C valence angle must be deformed 49.5° from the tetrahedral value. It is likely that some relief from the strain associated with the eclipsing of the hydrogens of cyclopropane is achieved by distortion of the H-C-H and H-C-C bond angles ... 

The distortion of the valence angles and the increase in interatomic distances are phenomena produced simultaneously during mechanical stress. The one determines the other, and their effects are summed. The overall result is activation of the backbone and transition of the material to a mechanically excited (tensioned or stressed) state exhibiting a higher sensitivity to chemical agents. This result is mainly related to the structure of the polymer and the chemical in contact with the... 

The units for the force constants are usually given in mdyn A-1 (bond length), mdyn A rad"2 (valence angle bending and out-of-plane distortion) and mdyn A (torsion angle deformation). 

This is the coupling between the change of the pseudorotation vector and totally hybridization compatible deformation of valence angles. The considered distortion produces the following HO transformation matrix (matrix H in eq. (3.27)) ... 

An analogous estimate can be applied to cyclobutane. In this case we consider the distorted methane molecule with one of the valence angles fixed at 90°. In our model, the response of the HOs to the deformation is proportional to the deviation of the valence angle from the tetrahedral one. The deviation of the C-C-C angle from the tetrahedral one in cyclobutane (19.5°) amounts to 40% of that in cyclopropane. Therefore, we can expect that about the same ratio will be observed for the deviations of the H-C-H valence angle from the tetrahedral one in the cyclobutane and cyclopropane molecules. In fact, the ratio got in the SLG-MINDO/3 numerical experiment is about 39%. 

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