THEORETICAL-STUDY OF THE O-H STRETCHING BAND IN 3-HYDROXY-2-METHYL-4-PYRONE

The infrared spectrum of 3-hydroxy-2-methyl-4-pyrone reveals an O-H st retching frequency roughly 200 cm(-1) lower than that of a typical alc ohol group. The frequency lowering results from intramolecular hydroge n bonding between the alcohol and ketone groups. In this work, the str etching and bending vibrations of the O-H group in 3-hydroxy-2-methyl- 4-pyrone are studied with a theoretical methodology;more rigorous than the conventional harmonic approximation. A two-dimensional potential energy surface in internal coordinates corresponding to different hydr ogen positions in the plane of the molecule is calculated with the use of the second order Moller-Plesset perturbation theory. To include al l possible variations in kinetic energy in a large amplitude vibration al mode, g-matrix elements with variable values are employed. The anal ytical expression for the Hamiltonian matrix elements of the two-dimen sional vibrational problem in a basis of shifted Gaussian functions is derived. Expectation values for the O-H stretch nuclear states are va riationally determined with the use of shifted Gaussian functions as t he basis set. The results of the calculations are compared with the re cent matrix-isolation infrared (IR) spectroscopic results. The calcula ted transition frequency corresponding to the in-plane O-H stretching is found to be in good agreement with the experimental-value. (C) 1998 American Institute of Physics.