Based on molecular geometry

Recently, Bacic et al.28 have studied the bending-stretching energy levels of HCN by SCF approximation with modes optimized within the class of elliptical (spheriodal) coordinates. This example will be examined here in some detail since (1) the improvement obtained by coordinate optimization in this case is very large and (2) this case illustrated how intuitive considerations based on molecular geometry, the shape of the potential surface, and so forth, can be useful in choosing a suitable parametrized class of coordinates. Whenever the trial set of parametrized coordinates is physically well motivated, the OC-SCF procedure of Eqs. (19)—(21) can be expected to yield excellent results. 

In these considerations on STL structure, one important aspect was not taken into account so far, namely, that of explicit stereochemistry. The STL database consists, as mentioned above, of 2D representations in the form of the SMILES string. It is at present not possible to include structural features based on molecular geometry, such as shape, charge distribution, etc. in our investigation on the molecular properties of STLs as a whole, since this would necessitate the generation of 3D structures with the correct stereochemistry for each of the 4861 molecules, which would only be possible by... 

Molecular geometry has a countless number of individual applications in interpretation of the chemical and physicochemical properties of chemical species. In this review we will deal only with interpretations which result from some general models based on molecular geometry of x-electron systems and which can be easily applied in other cases. 

The distance parameter, da. is the distance between the centers of electronic distribution in the donor and the acceptor orbitals, not a distance based on molecular geometry. Since electron density in molecules is highly polarizable. Equation (22) often has only qualitative value in assessing electronic coupling. 

The conclusions reached are the same as for the frontier orbital approach. The suprafacial 1,3-shift of hydrogen is forbidden but the suprafacial 1,5-shift is allowed. Proceeding to a 1,7-shift of hydrogen, it is found that the antarafacial shift is allowed. These conclusions based on transition state aromaticity are supported by MO calculations at the 6-31 level, which conclude that 1,5-shifts should be suprafacial while 1,7-shifts should be antarafacial. Theoretical calculations also find that the 1,3-shift of hydrogen should be antarafacial, but, in agreement with expectations based on molecular geometry, the transition state which is found is so energetic that it is close to a stepwise bond dissocation process. ... 

F(r) was also computed from ab initio wave functions in the framework of the HF/SCF method using 3-21G and 6-31G basis sets due to the large size ofLR-B/081, the calculation has as yet been performed on isolated molecular fragments, adopting a geometry based on molecular dimensions from X-ray diffraction studies. 

On this restricted basis, transition metal phosphines have been modeled with accuracies similar to those of other metal-heteroatom systems11531. A number of phosphine complexes are of interest in the area of asymmetric syntheses. Due to the requirement that the geometry and the force field of the relevant intermediates have to be known for a thorough study (see Chapter 7, Section 7.4) most of the reports in this area are only of a qualitative nature. Some of the investigations are based on molecular graphics analyses, and the evaluation of the predicted selectivity has been based on van der Waals terms alone[53,233,2341. 

Geometry based on molecular mechanics calculation. b Geometry of [Fe(tacn)2]CI356... 

Figure 8 Building a molecular model based on internal geometries (bond lengths /, bond angles 6, and torsional angles ). Each subsequent atom is added to the framework with respect to earlier situated atoms. The convention in many programs is that the x Cartesian axis is the horizontal axis on the computer screen, the y axis is vertical, and the z axis comes out of the computer screen toward the user.

The observation that the most photochemically reactive surface orientations all contain 101 facets suggests that the enhanced reactivity is not associated specificially with the bulk crystal orientation, but is a property of this particular surface plane. It is likely that there are special atomic configurations on this plane that either alter the efficiency with which photogenerated carriers are trapped at the surface or the rate at which they are transferred across the solid-liquid interface. Based on bulk geometry alone, there is nothing that sets the 101 plane apart from less reactive surfaces. On this surface, Ti cations are coordinated by five O, as they are on the (100) surface (which is inert). In the absence of higher resolution microscopy results, it is not possible to say if special molecular configurations are created by reconstruction or defect formation. 

By calculating molecular descriptors based on 3D geometry without a common orientation frame, the Comparative Molecular Moment Analysis overcomes the problems due to the molecular alignment. 

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