Influence on structure

The crystal structure of many compounds is dominated by the effect of H bonds, and numerous examples will emerge in ensuing chapters. Ice (p. 624) is perhaps the classic example, but the layer lattice structure of B(OH)3 (p. 203) and the striking difference between the a- and 6-forms of oxalic and other dicarboxylic acids is notable (Fig. 3.9). The more subtle distortions that lead to ferroelectric phenomena in KH2PO4 and other crystals have already been noted (p. 57). Hydrogen bonds between fluorine atoms result in the formation of infinite zigzag chains in crystalline hydrogen fluoride 

Pauling, The Nature of the Chemical Bond, 3rd edn., Chap. 12, Cornell University Press, Ithaca, 1960. 

Structural Inorganic Chemistry, 5th edn., Clarendon Press, Oxford, 1984, 1382 pp. 

0-H 0 248-290 (280) KH2PO4, NH4H2PO4, KH2ASO4, AlOOH, a-HI03, numerous hydrated metal sulfates and nitrates 

In summary, we can see that H bonding influences crystal structure by linking atoms or groups 

H bonding also vitally influences the conformation and detailed structure of the polypeptide chains of protein molecules and the complementary intertwined polynucleotide chains which form the double helix in nucleic acids.Thus, proteins are built up from polypeptide chains of the type shown at the top of the next column. 

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It is instructive to note the progressive trend to higher coordination numbers in the Group 16 dioxides, and the consequent influence on structure ... 

Bulky substituents at tetravalent silicon centers are the structural key element of sterically overcrowded compounds with extraordinary properties Inter- and intramolecular interactions of the bulky ligands can be studied in detail and allow an assessment of the ligands influence on structure and reactivity. 

For sodium and potassium chalcogenolates, donor influence on structural pattern has been explored with a special emphasis in donor hapticity. Thus, crown ether complexation allows the isolation of monomeric species, such as [K(SCPh3)(18-crown-6)Lra] (L=thf, CgH6, hmpa, n = 0.5 L=toluene, n = l),36 [K(SMes )(dibenzo-18-crown-6)(thf)],45 [K(STrip)(dibenzo-18-crown-... 

Ghirlando, R., J. Lund, M. Goodall, and R. Jefferis. 1999. Glycosylation of human IgG-Fc influences on structure revealed by differential scanning micro-calorimetry. Immunol Lett 68 47-52. 

Nevertheless, we cannot neglect the change in band structure as a result of contraction or distortion of the cluster octahedra. The misleading thing was the assumption that primarily electronic effects determine structure. It seems better if the relation is reversed namely, steric constraints have a decisive influence on structure, and the resultant structure coupled with the number of CVE is responsible for particular band structures. 

The type of alkylaluminum compound has only a secondary influence on structure in the polymerization of diolefins in contrast to its strong effect on the structure of polypropylene. An exception is AlEtCb, which, apparently in connection with its cationogenic character, with j3-TiCl3 induces polymerization to trans-1,4 polybutadiene and, even without transition metal compound, leads to formation of cyclized polyisoprene. Incidentally, this indicates that poly-butadiene is much more stable towards cyclization than polyisoprene. 

Boggs, J. (1987). Lipid intermolecular hydrogen bonding Influence on structural organization and membrane function. Biochim. Biophys. Acta 906 353. 

After presenting the sample preparation in Sect. 5.2, we give an introduction to the theoretical background in Sect. 5.3. In Sect. 5.4, we briefly review the electronic influence on structure and phase stability of crystalline Hume-Rothery phases. In Sect. 5.5, we discuss the properties of non-magnetic amorphous alloys of the type just mentioned. The electronic influence on structure (5.5.1) and consequences for the phase stability (5.5.2) are also discussed. Structural influences on the electronic density of states are shown in 5.5.3. Electronic transport properties versus composition indicate additionally the electron-structure interrelation (5.5.4), and those versus temperature, the influence of low-lying collective density excitations (5.5.5). An extension of the model of the electronic influence on structure and stability was proposed by Hdussler and Kay [5.21,22] whenever local moments are involved as, for example, in Fe-containing alloys. In Sect. 5.6, experimental indications for such an influence are presented, and additional consequences on phase stability and magnetic properties are briefly discussed. 

The electronic influence on structure and stability is easily explained by Fig. 5.3. The electronic states get raised as well as depressed at any zone boundary. If all the states up to infinite energy are occupied, the presence of the gaps has no effect on the total energy. This is different if the states are occupied up to g/2 or KPJ2 (g or Kpe = 2fcF). The decrease of the energy of the occupied states is not counterbalanced because the states above EF are empty a net... 

We have clearly demonstrated electronic influences on structure due to indirect interactions. In non-magnetic alloys, electric polarization of the electron cloud around localized charges (ions) causes Friedel oscillations and hence a preferred position of the ions. In magnetic alloys, evidence of another indirect interaction due to spin polarization around localized local moments causing RKKY oscillations has been shown. 

J, J. Kaufman, bit. ]. Quantum Chem., 16(2), 221 (1979). Quantum Chemical and Physico-Chemical Influences on Structure-Active Relations and Drug Design. 

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