Rychlewska Urszula, Rychlewski Jacek
Crystal structures of diastereomeric salts of tartaric acid and l,2-trans-diaminocyclohexane stimulated our interest in elucidating the mode of mutual interactions between the acid and the amine. For this purpose quantum mechanical methods were used to expound various modes of intermolecular recognition in vacuo, and the search through Cambridge Structural Database (CSD) was performed in order to characterize various hydrogen bonded ring motifs formed in crystals between the two components. The obtained results agree very well with the experimental observations, that the homochiral association of molecules is energetically favored over the heterochiral one. Mutual interactions between hydroxyacids and amines have been investigated using following simpler systems: glycolic acid, ammonia and methylamine in their neutral and ionic forms. Ammonia and amines tend to act as hydrogen bond acceptors from the carboxylic OH group in vacuo, which corresponds to the formation of salts in polar media. The cyclic hydrogen bond motif in which neighboring oxygen atoms are joined by the amine buckle is stable only in the system containing á-hydroxyacetic acid and the ammonium cation.