Influence of substituent groups

In addition to the antimony fluorides, silver, mercury, thallium, aluminium, zinc, zirconium, chromium and other fluorides [7] such as mercury(II) fluoride, vanadium pentafluoride [24] and various transition metal oxide fluorides [25] have been used in exchange processes, although much less widely. 

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Maleimides Alkyl and aryl maleimides in small concentrations, e.g., 5-10 wt% significantly enhance yield of cross-link for y-irradiated (in vacuo) NR, cw-l,4-polyisoprene, poly(styrene-co-butadiene) rubber, and polychloroprene rubber. A-phenyhnaleimide and m-phenylene dimaleimide have been found to be most effective. The solubihty of the maleimides in the polymer matrix, reactivity of the double bond and the influence of substituent groups also affect the cross-fink promoting ability of these promoters [82]. The mechanism for the cross-link promotion of maleimides is considered to be the copolymerization of the rubber via its unsaturations with the maleimide molecules initiated by radicals and, in particular, by allyfic radicals produced during the radiolysis of the elastomer. Maleimides have also been found to increase the rate of cross-linking in saturated polymers like PE and poly vinylacetate [33]. 

The fundamental influence of substituent groups on the photoconductivity within aceanthraquinoxaline derivatives is shown in Fig. 7 for two pyrazines that differ by a methyl group. 

Since the excited state is involved in the formation of the hydrogen bonded ring it is probably useless to speculate in detail about the influences of substituent groups using data from the customary reactions of organic chemistry. Photochemistry is the chemistry of excited and not of normal molecules. 

Previous investigations (Brady, 1949 Grayson, 1952 Bonner, 1952) in the Purdue laboratories were concerned with the influence of alkyl groups on the rate of ionization of phenyldimethylcarbinyl chloride. These studies indicated that first-order rate constants could be determined with high accuracy for the solvolysis reaction. Moreover, the entropies of activation were invariant in this series of halides. These considerations led to further study of other substituted phenyldimethylcarbinyl chlorides in an attempt to gain a further understanding of the influence of substituent groups on relative reactivity and as a possible model reaction for the assessment of parameters for electron-deficient reactions. 

It follows from the above that the influence of substituent groups on the ease of electrophilic attack on ring carbon atoms can be largely predicted from a knowledge of benzene chemistry. 

The calculated Rm values in Table III show the influence of substituent groups on the lipophilic character of cephalosporins. The Rm value of Compound II decreases more and more with the substitution of the naphthyl group by a benzene, a thiophene, or a furan ring as in Compounds V, VI, and IX. The hydrophilic character of V increases when an NH2 group is introduced into the side chain (Compound VIII) or when the OCOCH3 group is replaced by an OH (Compound X), or when the benzene ring is replaced by a Cl atom (Compound XI). 

INFLUENCE OF SUBSTITUENT GROUPS ON ADSORB ABILITY OF ORGANIC COMPOUNDS... 

The influence of substituent groups on adsorption is often viewed as furnishing clues as to the orientation. Thus, if the introduction of a particular group into a molecule enhances the adsorption, that group is presumed to be attached to the surface. Conversely, if... 

The influence of substituent groups and of other ions in solution (e.g., cupric, ferric, chloride, nitrite) has been examined. The work substantiates the reaction mechanism suggested by Waters (f). 

Then, to investigate the influence of substituent groups at C-6, the derivatives Aa (30), Ab (31), Ac (32) and Da (33) at were converted from casearins A (12) and D (15). As shown in Fig. 4, the inducement of acyl substituent at C-6 was found to cause marked reduction in the activity. These results support that bulkiness of the substituent at C-6 has the greatest influence on the activity. Also, the antitumor activity of casearins A (12), B (13), C (14) and F (17), which are major constituents in diterpenes of C. sylvestirs, against Sarcoma 180A ascites in mice are summarized in Table IV. Casearin C (14) showed the strongest effect in this bioassay. 

As with the first edition, the objective has been to provide an introduction to most of the major areas of chemical kinetics. The extent to which this has been done successfully wfll depend on the viewpoint of the reader. Those who study only gas phase reactions wiU argue that not enough material has been presented on that topic. A biochemist who specializes in enzyme-catalyzed reactions may find that research in that area requires additional material on the topic. A chemist who specializes in assessing the influence of substituent groups or solvent on rates and mechanisms of organic reactions may need other tools in addition to those presented. In fact, it is fair to say that this book is not written for a specialist in any area of chemical kinetics. Rather, it is intended to provide readers an introduction to the major areas of kinetics and to provide a basis for further study. In keeping with the intended audience and purposes, derivations are shown in considerable detail to make the results readily available to students with limited background in mathematics. 

The influence of substituent groups on biological activity can be partly due to steric effects. Hansch has introduced the Taft steric parameter (p. 217) to allow for this, giving an Equation of the form of (63). 

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