Structural Features of the Chain

Comparison of the heats of combustion of cycloalkanes (Table 9.1) shows that cyclopropane, cyclobutane, and cyclononane yield more energy per methylene group than the other cycloalkanes. This can be attributed to strain resulting from bond-angle distortion (Baeyer strain), eclipsed conformations (Pitzer strain), and trans-annular, repulsive van der Waals interactions. Common (five- and six-membered) rings and large (more than twelve-membered) rings have little or no strain. This 

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The present chapter thus far has been concerned solely with the structural features of the chain unit and its steric relations with neighboring units. It remains to consider certain aspects of the polymer structure on a larger scale, i.e., to consider the over-all pattern of interconnection of the units. 

Structural features of the chains give rise to physical properties that are also of considerable scientific interest. For example, the substituted Si atom and the unsubstituted O atom differ greatly in size, giving the chain a nonuniform cross section. This characteristic affects the way the chains pack in the bulk, amorphous state, which explains the unusual equation-of-state properties (such as compressibility). Also, the bond angles around the 0 atom are much larger than those around the Si, which makes the... 

We typically show the structure of a polymer by placing parentheses around the repeating unit, which is the smallest molecular fragment that contains all the structural features of the chain. A subscript n placed outside the parentheses indicates that the unit repeats n... 

Dependence (3.6) reflects the most important optical properties of the macromolecule the chemical features of the structure of the monomeric unit which determine the polarizability of the molecule (they are reflected in the values of p and Aa), the degree of ordering of the structure and conformation of the macromolecule, reflected in parameter A and in the type of change in the value of [n]/[Ti] with the molecular weight, and the function y(x). According to the theory elaborated by V.N. Tsvetkov [17, 18], such structural features of the chain as the polydispersion with respect to the conformations and the molecular chain thickness are taken into consideration in this dependence [17,18]. 

And third, since virtually all enzymes [67], particularly those that catalyze phos-phoryl-transfer reactions [68 74], possess structures with at least two, discrete, relatively rigid structural domains, or lobes, separated by a deep cleft, the cytoplasmic portion of the H -ATPase polypeptide chain in the model of Fig. 2 is drawn in such a way as to suggest this situation. The proposed interdomain cleft is indicated by the arrow. No additional structural features of the ATPase molecule are implied in the model. In regard to comparisons with the Ca -ATPase, it is of interest to note that the two cytoplasmic domains proposed in Fig. 2 correspond to the Cl and C2 domains in the model of Andersen and Vilsen [53]. 

A recently discovered subset of triple-stranded /l-helices from bacteriophage tail proteins (alternatively termed triple-stranded /1-solenoids ) represents another distinct group of /1-fibrous folds (Fig. 3B). In these structures, three identical chains related by threefold rotational symmetry wind around a common axis. These chains form unusual parallel /1-sheets with no intra- and only intermolecular -structural hydrogen bonding. Kajava and Steven (this volume) survey the distinguishing structural features of the known triple-stranded /1-solenoids, also documenting their notable diversity and differences in comparison to the single-stranded /1-solenoids. 

Another POLIDCASYR extension ensures that structural features of the backbone can be distinguished from those occurring in side chains. The system furthermore augments structure codes for polymers using a controlled vocabulary of keywords, such as epoxy resin , aminoplast or phenoplast . 

The Main Structural Features of the Carbohydrate Chains of Glycosaminoglycans... 

It is therefore quite easy to see why such a very large number of silicates is possible. In fact, the chemistry of these substances is now so developed that it can be classed next in importance to the chemistry of carbon compounds. It must not be assumed, however, that there is any direct relationship between the chemistry of silicates and that of carbon compounds. It is true that in both groups chains, rings and layers of atoms occur, but the structural features of the two groups are totally different. The silicon ions in silicates are always coupled to each other by oxygen ions, while in the carbon compounds the carbon atoms are joined directly to each other. Again, the bonds between carbon atoms are purely homo-polar, while the silicates must be regarded as partly ionic compounds. 

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