Crystal packing modes groups

Space Groups and Crystal Packing Modes, p. 1337 van der Waals Forces, p. 1550 X-Ray Crystallography, p. 1586... 

The internal symmetry of a crystal structure is described. The concepts of the unit cell and lattice are developed, leading naturally to a definition of symmetry elements and, hence, to the crystallographic space groups. The relevance of space groups and symmetry elements to the formation of the extended networks found in supramo-lecular chemistry is summarized. A discussion of common crystal packing modes follows, and the relevance of space group symmetry is discussed in this context. 

In p-PDA Et, a crystal transition is observed at 56 °C by DSC measurement. Packing modes of the crystals above and below 56 °C are nearly identical with only small differences in the orientation of the terminal ethoxycarbonyl groups. This explains why the crystal transition of p-PDA Et scarcely affects the polymerization behavior51. ... 

The simplest and most common way of obtaining resolved enantiomers on the preparative or commercial scale is by fractional crystallization of diastereoisomers. Flowever, because of lack of necessary information on the packing modes of chiral functional groups in diastereoisomeric environments, the processes involved are not properly understood and thus not fully exploited. 

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