Vibrational analysis of pyruvate ion molecules and estimation of equilibrium constants for their hydrogen isotopic exchange reactions

The infrared spectra (4000-200 cm^-1) of CH₃COCOONa and its four isotopic substitutions including ¹³C- and ¹⁸O-labeled modifications suspended in KBr disks were measured. Complete vibrational assignments were established on the basis of the isotope shifts of the fundamentals and a normal-coordinate analysis. From the normal-coordinate analysis a general valence force field involving 40 force constants, 7 of them being transferred from pyruvic acid, has been determined, which reproduced 90 experimental frequencies with a root-mean-squares deviation of 2.1 cm^-1. The valence force field was used to estimate fundamental frequencies which were not obtained from direct observation, and the reduced partition function ratios of the pyruvate ion molecules were evaluated by using the spectroscopic data including the predicted values of the fundamentals. The calculated equilibrium constants of some hydrogen isotopic exchange reactions between the pyruvate ion molecules were reported.