Classification Constitution, chemical

Classification by Chemical Constitution Classification of solvents according to chemical constitntion allows certain qualitative predictions. In general, a compound dissolves far more easily in a solvent possessing related functional groups than in one of a completely different nature (see table 3.11). A proper choice of solvent, based on the knowledge of its chemical reactivity, helps to avoid undesired reactions between solute and solvent. 

The details of the classifications and chemical structures of four types of natural phthalides are illustrated in Figs. (2-6). Most of the isolated natural phthalides belong to the 3-substituted phthalide type, which accounts for about 61% of the total known naturally occurring phthalides, and of these, non-alkaloid phthalides constitute the most important subtype due not only to their abundance in nature (75 compounds identified) but also their extensively reported pharmacological activities. The pharmacological activities of individual phthalides are discussed in the following Biological Activity Section. 

Dyes may be classified in a number of ways, including color, intended use, trade name, chemical constitution, and basis of application. Of these classification methods, chemical constitution and basis of application have been most widely used. Chemical constitution indicates the major chromo-phores present in the dye but does not indicate more than such structural aspects of the dye. A classification scheme for dyes has been developed and evolved for use by dyers which is based on the method of application... 

Fiber name Type/general classification Chemical constitution Ionic nature in dyebath... 

There is Httle correlation between classifications according to chemical type and appHcation properties. AppHcation classifications are of most practical usefulness to the dyer, and therefore the chemical constitutions of dyes are described here only briefly. Further detailed information on dye types (10) and their chemical manufacture (11) can be found elsewhere, and ia many other Eniyclopedia articles to which references are made. 

The Colourindex (5) assigns Cl generic names to commercial dyes. This Cl name is defined as "a classification name and serial number which when allocated to a commercial product allows that product to be uniquely identified within any Colourindex AppHcation Class." This enables the particular commercial products to be classified along with other products whose essential colorant has the same chemical constitution. 

Pigments are classified by an internationally recognised convention, published in the International Colour Index by the Society of Dyers and Colourists in Bradford, in association with the American Association of Textile Chemists and Colorists. The Index issues a generic name to chemically identical products (e.g., titanium dioxide is classified as C.I. Pigment White 6). Where structures are known, pigments are also given a constitution number (e.g., titanium dioxide has the constitution number Cl 77891).This number is reserved for the essential colorant, other ingredients, such as the carriers used in a masterbatch, do not affect this classification. 

Dyes are classified in accordance with either the chemical constitute or their application to textile fibers for coloring purposes. Table 1 gives this classification... 

This edition and the completely revised five-volume Third Edition (1971) established the Colour Index as the leading reference work for the classification of colorants, fully justifying the cognomen International belatedly added in 1987. The fourth revision (1992) of the Third Edition consisted of nine volumes. The original data on technical properties (Volumes 1-3) and chemical constitution (Volume 4) was supplemented (Volumes 6-9) at roughly five-year intervals. 

Publications have over the course of the years proposed several classification systems for organic pigments. Basically, it seems appropriate to adopt a classification system by grouping pigments either by chemical constitution or by coloristic properties. Strict separation of the two classification systems is not very practical, because the categories tend to overlap however, for the purposes of this book it is useful to list pigments according to chemical constitution. 

Two very similar molecules are two different physical objects [40], Hence, chemical/ structural comparison of similarity is a subtle and relative concept that acquires significance in a well-defined reference physical context. In other words, it is necessary to define in what respect and to what extent two different molecules are similar. Molecular series of specific and selective ligands interacting, in vitro and in equilibrium conditions, with a specific receptor constitute a sophisticated example of chemical similarity-diversity classification. This classification is based on the experimental binding affinity (AG°) values that quantify a particular molecular recognition phenomenon, which is, essentially, a noncovalent process [41]. This implies,... 

Enzymes constitute a large superfamily of proteins acting as biological catalysts capable of accelerating over a million-fold the rate of chemical reactions within cells. ° On the basis of the type of reaction catalyzed, enzymes are organized using a classification scheme that has prevailed for decades." ... 

A variety of drugs in distinct pharmacological and chemical classes can be considered under the broad classification as stimulants. Xanthines and methylxan-thines constitute a weak class of stimulants that includes caffeine, theophylline (aminophylline),and theobromine. Caffeine is freely available in coffee, colas, and certain over-the-counter pills. A low degree of tolerance develops to some of their effects and a mild withdrawal syndrome is observed following immediate cessation of their repeated use. 

Some other classification schemes are provided in a work by Kolthoff (Kolthoff, 1974). It is according to the polarity and is described by the relative permittivity (dielectric constant) e, the dipole moment p (in 10 ° C.m), and the hydrogen-bond donation ability Another suggested classification (Parker, 1969) stresses the acidity and basicity (relative to water) of the solvents. A third one (Chastrette, 1979), stresses the hydrogen-bonding and electron-pair donation abilities, the polarity, and the extent of self-association. A fourth is a chemical constitution scheme (Riddick et al., 1986). The differences among these schemes are mainly semantic ones and are of no real consequence. Marcus presents these clearly (Marcus, 1998). 

These chemical groups constitute one (vertical) axis of a diagram defining the Van Schmus-Wood classification system, as illustrated in Figure 6.3. The other (horizontal) axis is based on secondary characteristics. 

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