Crystal structures of anhydrous and hydrated N -benzyl-cinchonidinium bromide.

N -benzyl-cinchonidinium bromide, C 26 H 29 N 2 O + ·Br - , with the systematic name ( R )-[(2 S ,4 S ,5 R )-1-benzyl-5-ethenyl-1-azoniabi-cyclo-[2.2.2]octan-2-yl](quinolin-4-yl)-methanol bromide, is a quaternary ammonium salt of the cinchona alkaloid cinchonidine. This salt is widely used as a chiral phase-transfer catalyst and chiral resolution agent. Both classical and non-classical hydrogen-bonding inter-actions, as well as anion effects have been shown to play key mechanistic roles in the catalysis of cinchona alkaloids. In an effort to understand the effects of water on these inter-molecular inter-actions, the structures of anhydrous N -benzyl-cinchonidinium bromide, (I), and the sesquihydrate, C 26 H 29 N 2 O + ·Br - ·1.5H 2 O, (II), were determined.