Other Structural Features

If the chain backbone contains atoms that are unsymmetrically substituted, then stereochemical variability becomes possible. Stereochemical copolymers have repeat units that are chemically identical but stereochemically different, and in a sense these parallel the chemical copolymers already described. If substituted skeletal atoms in adjacent repeat units have the same atomic configuration, then the placement is said to 

The catalytic mechanism of amine oxidases can be fonnally divided into reductive and oxidative half cycles 

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As shown in the previous section the mechanical and thermal properties of polypropylene are dependent on the isotacticity, the molecular weight and on other structure features. The properties of five commercial materials (all made by the same manufacturer and subjected to the same test methods) which are of approximately the same isotactic content but which differ in molecular weight and in being either homopolymers or block copolymers are compared in Table 11.1. 

Additional keying information can come from certain other structural features which are present in a retron- or partial-retron-containing substructure. These ancillary keying elements can consist of functional groups, stereocenters, rings or appendages. Consider target structure 5... 

There are quite a number of crown compounds known which contain a thiophene or other sulfur-containing subunit. The reader is directed to the tables at the end of each chapter in order to locate these species. Because of the expense of including each structure under each possible category, some sulfur-containing compounds may not be listed in this chapter. It is hoped that the tables are well enough organized that the desired compound can be located if it is known by considering other structural features. 

Other hand, when the dislocation density is high, the dislocations do interact and they become tangled up with each other dislocation motion is then difficult and the material is therefore strong. The interaction of dislocations with each other and with other structural features in metals is a very complex field it is also, however, extremely important, since it greatly affects the strength of metals. 

Innumerable reactions occur in acid catalyzed hydrocarbon conversion processes. These reactions can be classified into a limited number of reaction families such as (de)-protonation, alkyl shift, P-scission,... Within such a reaction family, the rate coefficient is assumed to depend on the type, n or m cfr. Eq. (1), of the carbenium ions involved as reactant and/or product, secondary or tertiary. The only other structural feature of the reactive moiety which needs to be accounted for is the symmetry number. The ratio of the symmetry number of the... 

Apart from the role of substituents in determining regioselectivity, several other structural features affect the reactivity of dipolarophiles. Strain increases reactivity norbornene, for example, is consistently more reactive than cyclohexene in 1,3-DCA reactions. Conjugated functional groups usually increase reactivity. This increased reactivity has most often been demonstrated with electron-attracting substituents, but for some 1,3-dipoles, enol ethers, enamines, and other alkenes with donor substituents are also quite reactive. Some reactivity data for a series of alkenes with several 1,3-dipoles are given in Table 10.6 of Part A. Additional discussion of these reactivity trends can be found in Section 10.3.1 of Part A. 

Several of the copper and rhodium catalysts were compared in an intramolecular cyclopropanation.210 For the reaction leading to formation of a 10-membered ring, shown below, the copper catalysts gave higher enantioselectivity, but there were many subtleties, depending on ring size and other structural features in related systems. 

The previous sections in this chapter have tried to stress upon the significance of distribution of sequence lengths in polyethylene-based copolymers. The sequence length of interest in a system of ethylene-octene copolymers would be the number of methylene units before a hexyl branch point. As was discussed, this parameter has a greater impact on the crystallization behavior of these polymers than any other structural feature like branch content, or the comonomer fraction. The importance of sequence length distributions is not just limited to crystallization behavior, but also determines the conformational,... 

Despite the fact that the water-solubility of the s-fractions during the heating of their aqueous solutions (above the PST for the p-fraction) is an essential property of protein-like macromolecules, other structural features could also be responsible for such behaviour, including the following ... 

In the following, various Fe(III) compounds of R-substituted salicylaldehyde thiosemicarbazones will be discussed according to the criteria mentioned above, although it should be pointed out that a comparison of these materials may be rendered less meaningful due to the possible occurrence of different polymorphs. Moreover, upon variation of one substitution parameter, several other structural features may also be changed simultaneously. For instance, a change in outer-sphere cation or the introduction of a substituent at the salicylaldehyde moiety is frequently associated with increased hydration of the Fe(III) material. 

Additional keying information can come from certain other structural features which are... 

In conclusion, the new recycHng procedures described above offer virtually unhmited possibihties for optimization and catalyst engineering . The lengths and other structural features of the ponytails are easily varied. There are innumerable types of possible fluoropolymer supports, as well many additional classes of fluorous supports. Accordingly, a variety of further refinements and developments can be expected in the near future. 

Other structural features may influence the stereoselectivity of aldol condensations. One such factor is chelation by a donor substituent.68 69 Several /i-alkoxyaldchydcs show a preference for vyw-aldol products on reaction with Z-enolates. A chelated transition state can account for the observed stereochemistry.70 The chelated aldehyde is most easily... 

The rotational spectra of 3-methoxy-l,2,4-trioxolane (281) and 15 isotopomers containing H, and 0 point to a preferred conformation for both the ring and the methyl group and to other structural features. The C(3) atom is bonded to three oxygen atoms, for which the C—OMe bond distance is short (137.7 pm) as compared to C—(141.1 pm)... 

Other structural features of unsaturated-5(4//)-oxazolones can be deduced from crystallographic data including the effect on planarity of substituents on the exocyclic double bond. For example, 4-benzylidene-5(4//)-oxazolones show a completely planar conformation that favors strong electronic conjugation in both (2)990 isomers. The same effect has been reported for other 4-arylidene-... 

Other structural features that have acceleratory influences in the base hydrolysis of Co(III) systems are (i) the incorporation of a pyridine ligand in the coordination sphere and (ii) the incorporation of a flat secondary nitrogen donor system in the polyamine ligand skeleton (5) (structures C and D in Fig. 17). 

Importance of the Second Genetic Code Some aminoacyl-tRNA synthetases do not recognize and bind the anticodon of their cognate tRNAs but instead use other structural features of the tRNAs to impart binding specificity. The tRNAs for alanine apparently fall into this category. 

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