**4. Conclusions**

An experimental study of the phase behavior of chiral 3-(3,4-dimethylphenoxy) propane-1,2-diol **1** showed that enantiopure samples exist in a single stable crystalline form. In contrast, racemic **1** during crystallization under different conditions can exist in at least three modifications, namely stable racemic conglomerate (*R*+S)-**1** and two metastable racemic compounds α-*rac*-**1** and β-*rac*-**1**. With rapid crystallization from racemic solutions, all three phases can crystallize simultaneously.

Using the DSC approach, methods have been developed to obtain individual metastable phases, and all identified homochiral and racemic crystal modifications were ranked by energy. The IR spectroscopy and PXRD methods demonstrated the identity or similarity of all forms except β-*rac*-**1**, which is significantly different from the rest. The crystal structure of the forms (*R*)-**1** and α-*rac*-**1** was established by the SC-XRD method. It was found that supramolecular crystal-forming motifs in both forms are fundamentally the same and only symmetries differ. Preliminary information on the structure of β-*rac*-**1** phase was obtained by the PXRD approach.

Based on the information received, the experimental conditions for a successful direct resolution of racemic **1** into individual enantiomers by a preferential crystallization procedure were selected.

**Author Contributions:** Conceptualization, writing—review and editing, A.A.B.; methodology, DSC investigation, thermodynamics calculations, D.V.Z.; methodology, proofread the manuscript, resolution experiments, Z.A.B.; samples preparation and resolution, A.V.K.; XRD investigation, A.I.S.; XRD investigation, proofread the manuscript, A.T.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** The authors thank I.I. Vandyukova for valuable help with IR spectra analysis. The authors are grateful to the Assigned Spectral-Analytical Center of FRC Kazan Scientific Center of RAS for technical assistance in research.

**Conflicts of Interest:** The authors declare no conflicts of interest.
