The Aromatic CH/π Hydrogen Bond as an Important Factor in Determining the Relative Stability of Diastereomeric Salts Relevant to Enantiomeric Resolution − A Crystallographic Database Study

A systematic study was carried out to understand the principle underlying the process of enantiomeric resolution by the use of the Cambridge Structural Database. The crystal structures of fourteen pairs of diastereomeric salts, containing the mandelate anion, or its analogues, as the chiral acid component, were analyzed in the context of the aromatic CH/π hydrogen bond. The mean aromatic C−H···π distance parameters of the less‐soluble salts are shorter than in the more‐soluble ones. Also, the C−H···π‐ring access angle, on average, is more acute in the less‐soluble salts than in the more‐soluble ones. Nontrivial discrepancies, on the other hand, have been noted in case‐by‐case comparisons of the parameters of several pairs. It was concluded that the contribution from the aromatic CH/π hydrogen bond should at least be taken into account when considering enantiomeric separation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)