Chiral space group

In literature, SOHNCKE space-group types are often termed chiral space groups , which is not correct. Most chiral molecular compounds do not crystallize in a chiral (enantiomorphic) space group. For details see [86]. 

Do not call an achiral Sohncke space group (or space-group type) a chiral space group . Most chiral molecules do not crystallize in a chiral space group (p. 83). 

Broadly speaking, chiral space groups may be divided into two classes those that contain polar axes, for example, the commonly observed space groups P2, and C2 and those that do not, such as P2,2,2,. Crystal structures belonging to the latter class contain polar directions, but these do not coincide with the crystal axes. We shall focus on chiral crystals containing polar axes, although the method can in principle be applied to all chiral crystals. 

Consider for this purpose a chiral molecule, represented schematically as W-Y, packing in a crystal such that the vector W-Y tends to be parallel to the polar axis (66). (For the chiral space groups that do not contain polar axes, the... 

The monoclinic point symmetry 2 comprises a twofold axis and applies to the commonly observed monoclinic chiral space groups P2X and C2. 

Absolute asymmetric synthesis refers to the situation in which an asymmetric induction occurs in the absence of an externally imposed source of chirality [5]. Such reactions are invariably carried out in the crystalline state, where the asymmetric influence governing the enantioselectivity derives from the spontaneous crystallization of an achiral compound in a chiral space group. This phenomenon, which is analogous to the spontaneous crystallization of racemates as... 

We turn now to a presentation of our own research on the use of built-in or internal chiral auxiliaries for asymmetric induction in photochemical reactions in the crystalline state [28]. This work is a natural outgrowth of the work of Toda and coworkers on the use of external chiral host compounds for the same purpose discussed in Sect. 2.2. In both cases, the primary role of the chiral auxiliary is to guarantee the presence of a chiral space group for the ensuing solid-state photochemical reaction. 

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