Crystal conformation

Chain Conformation, Crystal Structures, and Structural Disorder in Stereoregular Polymers... 

By chance rather than by design, the third chapter in this volume also emanates from Israel. Bernard S. Green, Rina Arad-Yellin, and Mendel D. Cohen have surveyed organic reactions in the solid state from the standpoint of the stereochemist. In the first part of the chapter, the authors discuss the stereochemical consequences of the crystallization of conformationally mobile systems. Conformational, crystal-field, and hydrogen-bonding effects, among others, are responsible for the selective crystallization of stereoisomers that may not be dominant in solution. The second part of the chapter is concerned with the stereochemical consequences of chemical, and especially photochemical, reactions in the solid state. 

Table III. Gentiobiose Conformations Crystal Conformation Minimized in Four Potential Energy Functions...

The effect of the cyano substituent seems to dominate in 43 the bond opposite to it is the shortest91. The C—C (N) bond has the same length, 1.447 (4) A, as in other cyanocyclo-propanes (Section III.D). The phenyl group adopts the bisected conformation. Crystallization leads to a spontaneous resolution, which is rather rare among phenylcy-clopropanes, and a conglomerate of chiral crystals is formed91. 

The free ligand, or its protonated form dien-H ( = 0-3), has the potential to adopt the cis,cis (37), cis,trans (38) or trans,trans (39) conformations. Crystal structures of dien-H"+ (n = 2, 3) (Table 8) salts show that both the counter ion and degree of protonation determine which form is adopted. 

The sequence of amino acids in the long chain defines the primary structure of a protein. A secondary structure is determined when several residues, linked by hydrogen bonds, conform to a given combination (e.g., the a-helix, pleated sheet, and P-turns). Tertiary structure refers to the three-dimensional folded conformation of a protein. This is the biologically active conformation (crystal structure). A quaternary structure can result when two or more individual proteins assemble into two or more polypeptide chains. Conjugated proteins are complexes of proteins with other biomolecules, such as glycoproteins (sugar-proteins). 

Klebe, G., Graser, F., Hadicke, E. and Berndt, J. (1989). Crystallochromy as a solid state effect correlation of molecular conformation, crystal packing and colour in perylene-3,4 9,10-bis(carboximide) pigments. Acta Crystallogr. B, 45, 69-77. [263, 264]... 

Diphenyl-2,5-cyclohexadienone 3 exists as four polymorphs, labeled A-D, whose crystallographic details are summarized in Table 3-2 [14]. Polymorphs A-D are conformational polymorphs since they have different molecular conformers in their crystal structures. They are also concomitant polymorphs because they crystallized simultaneously from the same flask and under identical crystal nucleation and growth conditions. Forms B-D with multiple molecules in the asymmetric unit Z > ) may also be classified as conformational isomorphs. Such polymorph clusters with different molecular conformations, crystal packing and C—H - O... 

Figure 7. X-ray crystal structure of meso-octamethylcalix[4]pyrrole-methanol complex, 1-21916014. The calixpyrrole adopts a 1,3-alternate conformation. Crystal structure originally published in Allen, W. E. Gale, P. A. Brown, C. T. Lynch, V. M. Sessler,. L. j. Am. Chem. Soc. 1996, /18, 12471. Diagram produced using data from the Cambridge Crystallographic Database.

The reinforcement of polypropylene and other thermoplastics with inorganic particles such as talc and glass is a common method of material property enhancement. Polymer clay nanocomposites extend this strategy to the nanoscale. The anisometric shape and approximately 1 nm width of the clay platelets dramatically increase the amount of interfacial contact between the clay and the polymer matrix. Thus the clay surface can mediate changes in matrix polymer conformation, crystal structure, and crystal morphology through interfacial mechanisms that are absent in classical polymer composite materials. For these reasons, it is believed that nanocomposite materials with the clay platelets dispersed as isolated, exfoliated platelets are optimal for end-use properties. 

Keywords Mainchain liquid crystals Nematic conformation Crystallization Liquid-crystallization Transition entropies... 

Summary We present ab initio calculations and crystal structures of halo- and hydrido-substituted cyclodisilazanes as well as the synthesis and crystal structure of the first amino-chloro functional cyclodisilazane in the cw-conformation. Crystal structure determinations of cyclotrisilazanes are shown. 

Fig. 1.2 Solid form system illustrating long-range ordered (translational, orientational, and conformational) crystals on one end and completely disordered amorphous material on the other end. Solid forms can assume various length scale of order (long range, medium range, short range) and/or mesomorphic states (smectic, nematic)...

Fig. 6.14 Pseudo phase diagram of syndiotactic poly(styrene) in trans decalin. O crystallization of helix conformation crystallization of zigzag conformation melting of helix conformation melting of zigzag conformation. (From Deberdt and Berghmans (292))...

Form Crystal system Space group, lattice constants and number of chains per unit cell Molecular conformation Crystal density (g/cm )... 

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