Classification of molecules

Figure 3.10 A five-stage procedure for the symmetry classification of molecules.

The method for the classification of molecules into different point groups suggested by Zeldin (29) is outlined in Table 1-6. The method can be described as follows ... 

Several examples will be considered to illustrate the classification of molecules into point groups. Consider, for instance, the bent triatomic molecule of type AB2(H20) shown in Fig. 1-21. Following the rules... 

This collection of limiting factors clearly influences the quality of the model and its predictive power. In view of these sources of inconsistencies and errors in determining the intestinal absorption in humans, it is impressive that the quality of the model is as good as it is. In particular this model was shown to be of particular use as general model in earlier phase for classification of molecules. Any significant improvement is likely not to come from statistical or computational methods but from more consistent data on a broader collection of drug-like molecules preferably by an in vitro system eliminating some sources of experimental errors. 

Any two distinguishable molecules are said to be isomeric, if they have the same empirical formula and are based on the same collection of atoms. The hierarchic classification of molecules, according to isomerism, constitutional isomerism and stereoisomerism, is a centerpiece of the logical structure of chemistry [28]. 

Rather than introduce new words into an already confusing terminology, Bell (64) is of the opinion that the words acid and base should be confined to proton acids, and the Sidgwick classification of molecules as electron donor and electron acceptor (which is essentially equivalent to the Lewis classification of acids and bases) be employed, together with the categories of nucleophilic and electrophilic reagents as defined by Ingold (65). 

This concept allows the classification of molecules such as carotenoids, lipophilic vitamins, steroids, terpenes etc, as lipoids . Most researchers consider those molecules as separate groups and confine the term lipid to fatty acids, their derivatives and to substances that are closely related to their synthesis and function [1,2],... 

We shall now give examples of molecular and crystal structures based on 2-, 3-, and 4-connected systems. Although logically the cyclic and chain systems (corresponding to p = 2) should precede the polyhedral ones (p > 3) we shall deal with the latter first so that we proceed from finite to infinite groups of atoms. This kind of treatment cuts right across the chemical classification of molecules and 80... 

The general least-squares procedures can now be implemented in spreadsheets programmed with macros. Adjustments once impossible are now trivial. The classification of molecules to obtain electron affinities from half-wave reduction potentials is an example of a linear least-squares adjustment. The determination of the adiabatic electron affinity for acetophenone is an example of a nonlinear two-parameter least-squares procedure. The nonlinear least-squares adjustment of ECD to the expanded kinetic model is one of the major advances of the 1990s. 

This method transforms the frequency dimension into a property-weighted frequency dimension. The selection of atomic properties determines the characterization of the atoms within an RDF descriptor. Particularly, the classification of molecules by a Kohonen network is influenced by a decision for an atomic property. We can distinguish between static and dynamic atom properties. 

Orbital classification of molecules helped D. N. Shigorin to systematize molecules in terms of their spectral-luminescence properties85 89). Now spectral luminescence groups... 

The two alternatives for the classification of molecules having the same skeleton are ... 

When liquids contain dissimilar polar species, particularly those that can form or break hydrogen bonds, the ideal liquid solution assumption is almost always invalid. Ewell, Harrison, and Berg provided a very useful classification of molecules based on the potential for association or solvation due to hydrogen bond formation. If a molecule contains a hydrogen atom attached to a donor atom (0, N, F, and in certain cases C), the active hydrogen atom can form a bond with another molecule containing a donor atom. The classification in Table... 

Classification of molecules based on potential for forming hydrogen... 

---