The infrared spectra (4000-200 cm-1) of CH3CH2COONa and its seven 13C-isotopic modifications suspended in KBr disks were measured at 80 and 290 K. Excellent resolutions were obtained by recording the spectra at low temperature, from which all fundamentals except for the CO2 torsional mode were located without ambiguity. Complete vibrational assignments were proposed on the basis of qualitative empirical rules for group vibrations and characteristic 13C shifts of the fundamentals. A normal-coordinate analysis was carried out based on the experimental frequencies of the eight isotopic analogues. An approximate valence force field involving 34 force constants was defined within the framework of local-symmetry constraints. It has been found that the 34 force constants can be statistically well-determined through the least-squares refinement computation. The resulting force field reproduced 172 experimental frequencies with a root-mean-squares deviation of 1.9 cm-1. The composition of the normal vibrations from the symmetry coordinates has been given in terms of the potential energy distribution, from which additional important information on the assignments has been obtained. Particular attention was given to large values of the force constants associated with the carboxylate group, leading one to an understanding of the characteristic bond structure in the COO- fragment.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry