Crystal structures of anhydrous and hydrated N-benzylcinchonidinium bromide

N-benzylcinchonidinium bromide, C26H29N2O+·Br-, with the systematic name (R)-[(2S,4S,5R)-1-benzyl-5-ethenyl-1-azoniabicyclo[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 interactions, 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 intermolecular interactions, the structures of anhydrous N-benzylcinchonidinium bromide, (I), and the sesquihydrate, C26H29N2O+·Br-·1.5H2O, (II), were determined.