Classes of derivatives

In 1995 the 20th CGPM approved eliminating the class of supplementary units as a separate class in SI. Thus the new SI consists of only two classes of units base units and derived units, with the radian and steradian subsumed into the class of derived units of the SI. 

The second strategy is to replace the vinylene bridges of PPV (B) by a heteroatom possessing a lone pair that can participate in the n-conjugation [4]. Representative examples of this class of derivative (D) (Fig. 1) are the polyanilines and poly(p-phenylenesulfide) [la,b]. 

In reality, different classes of derivatives contribute the general definition of bis-dithiolene metal complexes, Scheme 8.72... 

The last class of derivatives able to mimic the haemoprotein function that we will consider is constituted by the series of square-planar Rh(I) and Ir(I) complexes with the Shiff base o-Ph2C6H4CH=NR, Scheme 6.25... 

The first carbon nanostructure that was covalently modified to alter surface properties was the C60 fullerene. After its discovery in the mid-1980s, numerous functionalization methods were developed for obtaining two important classes of derivatives, methanofullerenes and fullerene Diels-Alder adducts. 

Schiff base org chem RR C=NR" Any of a class of derivatives of the condensation of aldehydes or ketones with primary amines colorless crystals, weakly basic hydrolyzed by water and strong acids to form carbonyl compounds and amines used as chemical intermediates and perfume bases, in dyes and rubber accelerators, and in liquid crystals for electronics, shif, bas ... 

A number of 7V-carboxyalkyl and A-phosphonoalkyl substituted substrate analogue inhibitors have been examined [161,204-208]. These derivatives contain both the acidic carboxylate (or phosphonate) and basic amine functionalities in the vicinity of the scissile bond. Thus, they are capable both of electrostatic interaction with the active site Zn(II) and hydrogen bonding interactions with other active site residues. They are, however, only moderately potent collagenase inhibitors Table 8.18). The stereochemistry at the carbon atom to which the carboxylate moiety is bonded markedly influences the inhibitory potency of these derivatives ((197) vs. (198)). The phosphonate analogues of this class of derivatives have also been evaluated Table 8.18), but are not substantially better inhibitors than the carboxyl-ates. 

As one of the most reactive groups of carboxylic acid derivatives, acyl halides are very useful substrates for the preparation of the other classes of derivatives. For example, anhydrides may be synthesized by the reaction of carboxylic acid salts with an acyl halide. In this reaction, the carboxylate anion acts as the nucleophile, eventually displacing the halide leaving group. 

Section 7.8). Other classes of derivatives are thus most conveniently prepared from the sulfonyl chloride. Reaction with an alcohol leads to formation of a sulfonate ester. Two common sulfonyl chloride reagents employed to make sulfonate esters from alcohols arep-toluenesulfonyl chloride, known as tosyl chloride, and methanesulfonyl chloride, known as mesyl chloride (see Section 6.1.4). Note the nomenclature tosyl and mesyl for these groups, which may be abbreviated to Ts and Ms respectively. 

Some ammi no-platinum compounds have been described containing turn platinum atoms in the molecule. These should belong to tire same class of derivatives as the polynuclear cobalt-ammincs and cliromi-animines, but so far they have not been fully investigated. 

Another class of derived quantities is represented by the coefficients in diverse physical equations, e.g., transfer equations. They are established by the respective equations and determined via measurement of their constituents (e.g., heat and mass transfer coefficients). 

Chemical Properties and Derivatives. There have been thousands of rifamycin derivatives prepared in an attempt to obtain a broader-spectrum antibiotic having good oral absorption. Rifamycins B, O, and S have served as starting materials tor the preparation of numerous classes of derivatives. Several of the semisyntheUc derivatives are more active, have a broader spectrum of biological activity, and are therapeutically more effective than the parent antibiotics. 

A promising class of derivatives is the 8,10-dideaza series, the subject of intensive investigation. Adapting previously described methodology for 8-... 

Nitrogen-containing heterocycles are of obvious interest in the context of prebiotic chemistry. This is the reason why we will now consider this class of derivatives. The first so-called evidence for the presence of 4-hydroxypyrimidine and 4-hydroxy-methyl-pyrimidine in Murchison was published in 197158These results were divergent from those of previous studies performed on Orgueil samples where adenine, guanine, j-triazines and guanylurea were detected 59 60). 

As this chapter covers the most important class of thiazoles by the number of products and references, it is virtually impossible to treat in detail every class of derivatives. The mechanism-oriented approach to reactivity and the detailed tables at the end of the chapter should, however, permit easy extrapolation to most other compounds. 

The present Section is mainly concerned with differences of stability between the two classes of derivatives and any variations within each class. Their stability toward hydrolytic agents has frequently been examined, and, for the thiocarbonates, the thermal stability has also received attention. These studies have, in general, been neither exhaustive nor quantitative, and comparative data are directly available for certain cellulose derivatives only. The progressive replacement of the oxygen atoms in a neutral carbonic ester by sulfur appears to lead to a decrease in the sensitivity to alkali and an increase in the sensitivity toward acids, water, and heat. As expected, the acid esters are less stable than their neutral analogs toward the last-named agents. 

A relatively novel class of derivatives is obtained by the covalent incorporation of organometallic moieties into cellulose. For example, cellulose ferro-cenyl derivatives have been prepared by esterification of cellulose with an intermediate derived from ferrocene carboxylic acid and triphenyl phosphite in the presence of pyridine [84]. An enzymatically cleavable cellulose ester has been developed [85], and prodrugs have been coupled to the hydroxyl or carboxyl functions of C-terminal aromatic amino acids of cellulose peptide derivatives for controlled release applications [86]. 

The intermediate derived from naphthalene-1,3,6-trisulfonic acid along with the class of derived dyes are shown in Table 8.3 [11]. 

Esters.—It will be recalled that in the aliphatic series there are two classes of derivatives of sulphuric acid. When sulphuric acid reacts with an alcohol neutralization takes place between the alcohol, as a base, and the sulphuric acid water, H—OH, is eliminated and a compound known as an ethereal salt or ester is obtained. 

Two important classes of derivatives of the azo compounds which include some very valuable dyes are the amino azo and hydroxy azo compounds. The latter which are also called oxy azo compounds are derivatives of the azo compounds resulting from the substitution of one or more hydroxyl groups in the rings. 

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