Abstract
The crystal structures of the diastereomeric salts formed between cinchonine and mandelic acid have been analysed. The more soluble of the two salts is cinchoninium (S)-mandelate, C19H23N20 +.C8H703--, Mr = 446.55, monoclinic, P21, T= 110 (1) K, a = 11.2478(10), b=7.0880(6), c=14.684(2) A, /3= 99.068 (7) °, V = 1156.0 (4)/~3, Z = 2, Ox = 1.283 g cm -3, A(Cu Ka) = 1.54184 A, # = 6.57cm-1, F(000)=476, R=0.029 for 2338 observed reflections. The less soluble salt is cinchoninium (R)-mandelate, CI9H23N20 +.CSH7Of, Mr = 446.55, orthorhombic, P212121, T = 122.0 (5)K, a = 12.078 (4), b = 17.423 (2), c = 22.136 (4),~, V= 4658 (3) A 3, z = 8, Dx = 1.273 gcm- 3, A(Cu Ka) = 1.54184 ,~, /1, = 6.52 cm- ~, F(000) = 1904, R = 0.055 for 4125 observed reflections. In the (R)-mandelate salt one of the two independent cinchoninium cations displays disorder of the --CH=CH2 moiety. Apart from variations in the conformation of the vinyl group the cinchoninium cations are alike. The difference in conformation of the (R)- and (S)mandelate ions can be related to differences in the hydrogen-bonding systems. Interionic interactions in the S salt stabilize it relative to the R salt. The differences in the melting enthalpies and entropies of the two diastereomeric salts are related to their structural differences.
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