Ab initio and DFT calculations of the structure and vibrational spectra of trigonelline

The geometries, frequencies and infrared intensities of the vibrational bands of trigonelline its manohydrate and dimer have been computed by the MP2 and B3LYP approaches using the cc-pVDZ and 6-31G(d,p) basis sets. The computed geometry of the pyridine ring is slightly affected by hydration and dimerization, and satisfactorily agrees with the X-ray data. In contrast, the geometry of the COO group changes significantly on hydration and dimerization. All the measured IR bands were assigned in terms of the calculated vibrational modes. Most computed bands are predicted to he at higher wavenumbers; than the experimental bands. R.M.S. deviation between the experimental and the calculated harmonic frequencies is 69 cm(-1) for all of the bands, and 46 cm(-1) for all bands except those corresponding to nu(OH), delta(OH) and nu(CH). (C) 2002 Elsevier Science B.V. All rights reserved.