*3.4. IR Investigations of All the Detected Phases*

Differences in the vibrational spectra of crystalline modifications formed by identical (accurate to configuration) molecules, primarily, although not always explicitly, reflect differences in the internal organization of crystals. Some time ago, we proposed a quantitative and at the same time graphic way of pairwise comparison of such spectra [45,46]. In this case, the correlation coefficient between the spectral curves acts as a quantitative measure of the coincidence of the spectra, and the correlation trajectory, which degenerates into a straight line oriented along the main diagonal of the graph when the spectra are completely identical, serves the purposes of visibility. In Figure 5, the spectrum of the pure racemic conglomerate (*R*+*S*)-**1** is alternately compared with the spectra of pure samples (*R*)-**1**, α-*rac*-**1** and β-*rac*-**1**.

**Figure 5.** Comparison of the IR spectrum of conglomerate (*R*+*S*)-**1** (red curve) with the spectra of samples (*R*)-**1** (**a**), (blue curve), α-*rac*-**1** (**b**), (violet curve), and β-*rac*-**1** (**c**), (olive curve).

It can be seen from the figure that the internal organization of the conglomerate crystals and the enantiopure sample practically coincide, and the forms (*R*+*S*)-**1** and α-*rac*-**1** are structurally close. At the same time, both the correlation coefficient **R** and the appearance of the correlation diagram (the right fragment of the figure) indicate significant differences in the crystalline organization between these modifications and the metastable racemic phase β-*rac*-**1**. The information on similarities and differences revealed in this way is in complete agreement with the above data on the energy of crystalline modifications of diol **1** and with the results of XRD studies below.
