A density functional theory derived force field for the dicyano-pyridinium methylide

SUMMARY A Fourier transform Raman spectra of solid dicyano-pyridinium methylide is reported. Observed frequencies for normal modes are compared with those calculated from normal coordinate analysis carried on the basis of an ab initio force field for dicyano-pyridinium methylide. This force field has been deduced fromab initio calculations based on the density functional theory approach. A careful scaling of the internal force constants using correct vibrational assignments is shown to predict quite accurately our experimental vibrational frequencies and the potential energy distribution for dicyano-pyridinium methylide. Thus, a general valence force field for cycloimmonium ylides is constructed on the basis of structure and vibrational spectra of dicyano-pyridinium methylide. ©1997 by John Wiley & Sons, Ltd.