Polymorphism with a Varying Type of Stereoisomeric Recognition: Two Crystal Modifications of Isobornylacetamide

Two known polymorphic modifications of racemic isobornylacetamide (C2/c (1a) and P2₁/n (1b) space groups) are prepared quantitatively for the first time and are characterized in comparison with each other using physico-chemical methods such as low-temperature XRD, DSC, and IR spectroscopy. The alternation of molecules of opposite configurations in the H-bonded chain of the crystal of 1b leads to the formation of stronger hydrogen bonding than in the homo-chiral chain of the crystal of 1a (as is indicated by the XRD and IR spectroscopy data on the H-bond parameters) and a larger number of secondary interactions. Thermochemical parameters of both modifications are obtained for the first time by DSC, and it is shown that the 1b polymorph is thermodynamically preferable in the melting point region.