Assignment of the low frequency modes of the catalytic surface modifier cinchonidine and its diastereomer cinchonine

The surface modifier cinchonidine and its diastereomer cinchonine have been investigated and their vibrational spectra assigned, below 1000 cm−1. Scaled DFT ab initio calculations with PED assignments were in good agreement with neutron and optical vibrational spectroscopy. 4-Quinolinol, and quinuclidine hydrochloride were used as model compounds and their eigenvectors were compared with those of the parent molecules to aid in the assignments. This is the first low frequency assignment attempted on these systems and extends our understanding of the vibrations of the enantioselective promoters into regions not normally exploited by conventional spectroscopy.