Chemical structure definition

Clearly, the next step is the handling of a molecule as a real object with a spatial extension in 3D space. Quite often this is also a mandatory step, because in most cases the 3D structure of a molecule is closely related to a large variety of physical, chemical, and biological properties. In addition, the fundamental importance of an unambiguous definition of stereochemistry becomes obvious, if the 3D structure of a molecule needs to be derived from its chemical graph. The moleofles of stereoisomeric compounds differ in their spatial features and often exhibit quite different properties. Therefore, stereochemical information should always be taken into ac-count if chiral atom centers are present in a chemical structure. 

Reactions can be considered as composite systems containing reactant and product molecules, as well as reaction sites. The similarity of chemical structures is defined by generalized reaction types and by gross structural features. The similarity of reactions can be defined by physicochemical parameters of the atoms and bonds at the reaction site. These definitions provide criteria for searching reaction databases [23],... 

Although it is very difficult and probably of little value to produce an adequate definition of the word plastics , it is profitable to consider the chemical structure of known plastics materials and try to see if they have any features in common. 

Homogeneous catalysts are very often known as examples of single-site catalysts characterized by complete structural definition and (presumably) complete knowledge of the chemical processes occurring at their catalytic centers. It is a matter of fact that the homogeneous catalysts are molecular complexes constituted by an active core containing a single active atom (of-... 

Reaction mechanisms in chemistry are often written as a sequence of chemical structures, and such structures are referred to as reactive intermediates. Indeed, these intermediates often correspond to local minima on the potential energy curve—as shown in Figure 9.1—but need not do so, and the definition of a reactive intermediate... 

These recent results for dense polybead systems are very encouraging. One must wait for tests on realistic polymers with complicated chemical structures and side groups, however, before definitive conclusions can be drawn. The scaling law for the embedding algorithm has to be explored in more detail for the most cumbersome polymer structures. 

Definition of potential paths for chemical structure changes to improve the targeted properties... 

It should be clear by the definition given so far that the carbene-analogous state is limited to molecular species. The oligomer of EX2 (EX2)n is, of course, much more stable than EX2 in every respect. It should nevertheless be noted that also the oxidation number does not change in going from the monomer to the polymer the chemical, structural, and electronic properties of these species are completely different. 

The above-mentioned statistical characteristics of the chemical structure of heteropolymers are easy to calculate, provided they are Markovian. Performing these calculations, one may neglect finiteness of macromolecules equating to zero elements va0 of transition matrix Q. Under such an approach vector X of a copolymer composition whose components are X = P(M,) and X2 = P(M2) coincides with stationary vector n of matrix Q. The latter is, by definition, the left eigenvector of this matrix corresponding to its largest eigenvalue A,i, which equals unity. Components of the stationary vector... 

The development of a quantitative theory of a free-radical copolymerization implies the derivation of equations for the rate of the monomers depletion and the statistical characteristics of the chemical structure of macromolecules present in the reaction system at the given conversion p of monomers. Elaborating such a theory one should take into account a highly important peculiarity inherent to any free-radical copolymerization. This peculiarity is that the characteristic time of a macroradical life is appreciably less than the time of the process duration. Consequently, its products represent definitely... 

The importance of ultraviolet absorption spectroscopy as a tool for the elucidation of the chemical structure of organic compounds is well established. Although it has been extensively used in lignin research, as yet definite conclusions have not been attained. 

Define any unusual terms use ISO definitions wherever possible. Quote sources. Chemical structures can be included here if relevant. 

Ashby J, Tennant RW. 1990. Definitive relationships among chemical structure, carcinogenicity and mutagenicity for 301 chemicals tested by the U.S. NTP. Mutat Res 257 229-306. 

Although pyrethroids have been developed without a concrete definition, it is quite difficult to define this group of compounds based on their chemical structures. As such, I would like to propose the following definition ... 

It would appear that the specific action of an enzyme upon its substrate is conditioned by a definite chemical structure and spatial arrangement of the constituent polar and non-polar groups of the enzyme protein as well as by the constitution and configuration of the substrate. In some cases an enzyme interacts with one chemical compound only. For example, galactokinase extracted from Saccharomyces fragilis (grown on whey) catalyzes the transphosphorylation between adenosine triphos-... 

The pharmacophore concept, like that of molecular/chemical structure, assumes different meanings, and consequently different definitions, according to the accuracy and resolution level of its information content. 

The medicinal chemist expects to find that a review written specifically for him will he mainly concerned with a discussion of structure/activity relationships. In the case of the antihypertensive activity of the (3-blockers such a discussion is not possible since no direct comparative activity data is available either from the laboratory or the clinic (the few comparative clinical studies are in no way definitive - see later). It is however possible to approach the problem somewhat indirectly and consider the influence of chemical structure on those pharma -cological properties which appear most relevant to the specific clinical effect. I propose therefore to -... 

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