Quininium (S)-2-chloro-n-butyrate

The title compound, C₂₀H₂₅N₂O₂⁺·C₄H₆ClO₂^-, was crystallized by evaporation of an acetone solution and this is the first published report describing the structure of a crystal phase for this salt. Quinine is commonly used as a resolving agent for classic resolution. The anion was of inter­est because it has several desirable properties for absolute configuration studies, viz. strong acidic pK_a for salt formation, a somewhat heavy atom for strong diffraction and a known stereocenter.