Crystal and molecular structure of quinidine.

The structure of the free base quinidine was determined by single crystal X-ray diffraction. Quinidine crystallizes from absolute ethanol as the ethanolate, with the molecular formula C20H24N2O2.C2H6O and molar mass 370.491 units. It crystallizes in the orthorhombic space group P212121 with unit cell dimensions a = 1321.1(3), b = 989.3(2), and c = 1651.5(3) pm. The measured density was 1.15 g/cm3; the density calculated for Z = 4 was 1.164 g/cm3. The diffraction data were collected by using MoKalpha radiation. A final R value of 0.055 was obtained. Evidence for intermolecular hydrogen bonding was found. The crystal analysis is in agreement with the structure proposed by other methods. The absolute configuration is based on the published structure of 10-bromo-10,11-dihydroepiquinidine.