Theoretical and experimental study of vibrational spectra of two polymorphic 4-hydroxy-1-methylpiperidine betaine hydrochlorides

The molecular geometries, harmonic frequencies and intensities of the vibrational bands of α and β polymorphs of 4-hydroxy-1-methylpiperidine betaine hydrochloride (α-HO-MPBH·Cl, β-HO-MPBH·Cl) and their deuterated derivatives have been calculated with the B3LYP/6-31G(d,p) level of theory. The calculated frequencies are compared with the solid FTIR and Raman spectra. Unequivocal assignments of the experimental infrared bands are performed on the basis of the potential energy distribution (PED).