1 : 3 and 1 : 2 discrete compounds are verified in two chiral systems and discussed with respect to known cases in the literature.

Two model compoundsvaline C 5 H 11 NO 2 (L-Val) and isoleucine C 6 H 13 NO 2 (L-Ile)were chosen to study isomorphism of the compounds formed by enantiomeric molecules having similar shapes, but differing in the number of chiral centers. The X-ray powder diffraction method was applied to investigate samples with various ratios of valine and isoleucine crystallized from aqueous solutions by cooling and isothermal methods. Limited solid state miscibility between valine and isoleucine was established. A non-equimolar discrete compound with the molecular ratio Val:Ile = 2:1 (V 2 I) has been discovered, and its crystal structure was determined. Accordingly, the corresponding regions of solid solutions and two-phase areas in-between were distinguished. Solubility data in water support the phase behavior in the system.

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X-Ray diffractometry was employed to investigate the possibility of formation of non-equimolar discrete compounds in the chiral system of malic acid S-and R-enantiomers. Samples studied were mixtures of single enantiomers or an enantiomer and the various polymorphs of the racemic compound. From samples prepared via recrystallization of the melt and grinding of initial reactants, it is demonstrated that the malic acid enantiomers can form stable stoichiometric compounds in S:R ratios of 3:1 and 1:3. Compared to the known racemic and pure enantiomer phases, the corresponding compounds S 3 R/SR 3 are characterized by a proper powder diffraction pattern and melting point.

Equimolar and non-equimolar heterocompounds of amino acids are examined with a common approach considering their molecular dimers, side chain structures and conformations.