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In four of the five crystalline modifications of the muscle relaxants mephenoxalone 3 and metaxalone 2, chain supramolecular motifs of three different types are realized. The centrosymmetric cyclic dimer, which is considered typical of amides, was found only once. To clarify the nature of the emerging supramolecular synthons, the set of 119 crystal structures of 1,3-oxazolidin-2-one 1 derivatives, to which drugs 2 and 3 belong, were selected from the Cambridge Structural Database. Analysis of the sample showed that oxazolidinone fragments predominantly form closed ring synthons in racemic crystals, whereas linear chains are typical for enantiopure ones. Thus, in the case of chiral objects, the transition from racemic to enantiopure crystal serves as a powerful tool for designing crystals with a given organization of supramolecular synthon. Two earlier unidentified kryptoracemates (false conglomerates), QEFJAP and QEFJUJ, were found among the analyzed set. Apparently, these are the first representatives of oxazolidinones exhibiting this rare property.

Thermochemical properties of binary mixtures of the popular chiral drug timolol maleate (TM) were investigated by differential scanning calorimetry. It was found that there are no eutectic points on the melting phase diagram, and the enantiomeric components form a continual set of solid solutions over a wide concentration range. The crystal structure of heterochiral racemic TM is essentially isostructural with that of the homochiral (S)-TM, having close cell parameters but containing a crystallographic inversion centre. The crystal structure of the homochiral TM contains two symmetry independent molecules in the unit cell. These molecules have different conformations but are approximate mirror images of each other in the crystal lattice. Within the homochiral crystals only one site of two changes its nature in the heterochiral crystals. The solid solution of TM could be treated as the solid solution of a regular racemic compound and a pure enantiomer.

According to differential scanning calorimetry data ortho-, meta-, and para-tolyl glycerol ethers 1–3 form thermodynamically most stable crystal phases during solution crystallization. For all members of the series the crystal phases formed during melt crystallization have different thermodynamic characteristics from those of the stable ones. Binary melting diagrams were constructed for the stable solid phases; on this basis it was found that 1 is prone to spontaneous resolution, and 2 and 3 form stable solid racemic compounds, the Gibbs energy of formation for which are found to be −2.70 and −2.43 kJ mol−1. Solution grown single crystals of 1–3 were investigated by an X-ray diffraction method. The principal supramolecular crystal formative motifs were revealed: 1D columns for 1 and scal-2, 2D bilayers having developed a 2D system of intermolecular hydrogen bonds (IMHB) for rac-2 and rac-3, and 2D bilayer having 1D spiral IMHB organization for scal-3. The possible reasons preventing the solid racemic compound formation in the case of 1, and the spontaneous resolution manifestation in the cases of 2 and 3 are disclosed. It was demonstrated that, from the whole family of tolyl glycerol ethers, only scal-3 samples are capable of supramolecular gels formation. This property is connected with the peculiarities of the scalemic 3 crystal packing.

For a family of chiral terminal ortho-alkylphenyl glycerol ethers [alkyl = Me (1), Et (2), n-Pr (3), i-Pr (4), t-Bu (5)] nine different crystalline modifications have been obtained and investigated by X-ray analysis. All possible types for chiral compound crystallization, including a very rare type of false conglomerate (polymorph of rac-4.1) and extremely rare case of anomalous conglomerate (metastable form of rac-5) have been found within this set. Three tested substances crystallize as normal conglomerates, while two are capable of forming normal racemic compounds. Centrosymmetrical dimers of enantiomers, which are typical for most racemates, are absent in all the investigated crystals. The samples of the enantiopure compound 2 and 3 form stable supramolecular gels in hydrocarbon solvents. Some assumptions have been made linking the features of the molecular and crystal structures in the investigated series.

p-Tolyl glycerol ether not belonging to any of the known gelator families forms stable transparent gels in hydrocarbon media showing very good quantitative characteristics of gelling abilities, which are, in turn, strongly dependent on the chiral characteristics of the gelator. The crystal packing differences between the rac- and scal-substances could be the reason for such behaviour.