A list of organic kryptoracemates

Abstract

A list of 181 organic kryptoracemates has been compiled. This class of crystallographic oddities is made up of racemic compounds (i.e. pairs of resolvable enantiomers) that happen to crystallize in Sohnke space groups (i.e. groups that include only proper symmetry operations). Most (151) of the 181 structures could have crystallized as ordered structures in non-Sohnke groups. The remaining 30 structures do not fully meet this criterion but would have been classified as kryptoracemates by previous authors. Examples were found and checked with the aid of available software for searching the Cambridge Structural Database, for generating and comparing InChI strings, and for validating crystal structures. The pairs of enantiomers in the true kryptoracemates usually have very similar conformations; often the match is near-perfect. There is a pseudosymmetric relationship of the enantiomers in about 60% of the kryptoracemate structures, but the deviations from inversion or glide symmetry are usually quite easy to spot. Kryptoracemates were found to account for 0.1% of all organic structures containing either a racemic compound, a meso molecule, or some other achiral molecule. The centroid of a pair of enantiomers is more likely (99.9% versus 99% probability) to be located on an inversion center than is the centroid of a potentially centrosymmetric molecule.

Blending Gelators to Tune Gel Structure and Probe Anion‐Induced Disassembly

“…The alkylene chains all adopt a parallel all- trans conformation and the amino acid ester substituents are located almost perpendicular to the long molecular axis, engaging in CH⋅⋅⋅O hydrogen bonding interactions[26] with adjacent molecules. The glycine derivatives 1 and 3 crystallise in centrosymmetric space groups, whereas the chirality of the l -alanine derivatives in 2 and 4 is evident in their adoption of the Sohnke space groups[27] P 1 and P 2 1 , respectively. The representative structure of 1 form A is shown in Figure 2 a.…”

4-Benzoylamino-3-hydroxybutyric Acid, Historically First “Anomalous Racemate”: Reinvestigation

“…In more detail this phenomenon (under the name of kryptoracemates) was described by Fábián and Brock; kryptoracemates were found to account for 0.1% of all organic structures containing either a racemic compound, a meso molecule, or some other achiral molecule. 11 The third and the last group of conglomerates comprise those, in which the asymmetric unit is formed by molecules of various enantiomers, but in unequal amounts. Thus the enantiomeric purity of the asymmetric unit may be in principle any rational number between 1> ee as.u > 0.…”

Towards a Universal SMILES representation - A standard method to generate canonical SMILES based on the InChI

“…The authors extracted this layer, and developed an algorithm that generated all of the tautomers consistent with it. The layered structure of the InChI can be exploited to identify isomers of various types; in a crystallographic study, Fábián and Brock [35] used the enantiomer layer to identify a particular class of racemic crystal, kryptoracemates, where the enantiomers are not related by space-group symmetry.…”