Vibrational band assignments for the chiral modifier cinchonidine: Implications for surface studies

Vibrational assignments for the chiral molecule cinchonidine using a combination of experimental vibrational spectroscopic measurements and ab initio computational methods are reported. Several bands in both the IR and Raman spectra are identified as useful in providing information regarding the mode of adsorption of cinchonidine on metal surfaces, a system of great relevance to enantioselective catalysis. In particular, vibrational modes associated with the quinoline group can be used to diagnose the degree of tilt of the molecule with respect to the plane of the substrate. The use of this information for the study of cinchonidine adsorption on polycrystalline platinum with both reflection-absorption infrared spectroscopy (RAIRS) and surface-enhanced Raman spectroscopy (SERS) is discussed. Adsorption geometries for cinchonidine on platinum at low and high concentrations are reported.