Formic Acid vibrational assignments

In. a number of cases sub-maxima associated with vXH bands have been interpreted in this fashion and in the case of the carboxylic acid dimers this question has been investigated in some detail [4]. A prominent satellite band accompanying the main vOH bands has been assigned to an overtone of the <5QH vibration, and it has been possible to explain formally most of the multiplicity of peaks in the rOH band of formic acid in Fermi resonance terms. Although it is possible that some of these peaks correspond to Stepanov-type sub-bands, no convincing series of this type can be picked out. There seems little doubt that in many cases a considerable number of sub-bands in the rXH region are to be interpreted in terms of Fermi resonance [5, 43,... 

Most fundamental work on the vibrational spectra of azoles appeared in the period 1960-1980. Examples of more recent work include (i) a complete assignment of the gas-phase IR spectrum of indazole (93JCS(F1)4005) (ii) IR spectral data were used to determine the enthalpies of 0—H. . . N and N—H. . . O bonds in complexes of formic acid and 3,5-dimethylpyrazole (87MI301-01) (iii) the vibrational assignment of the Raman spectrum of polycrystalline pyrazole (92MI301-01) based on 3-21G calculations. 

Table 3-XVI presents some of the assignments for these modes in the monomeric and dimeric states. The relative shifts are uniformly high, near 0.1, with the notable exception of that of deuteroformic acid. This deviation cannot be discounted, because the assignments of formic acid are among the least ambiguous. Nevertheless, we can generalize that most workers propose that two vibrations of carboxylic acids involve Vb and that both of these vibrations move upward in frequency up>on H bond formation. The magnitudes of Lvb/Vb suggest that Vb may be almost as sensitive to the H bond perturbation as v, Av,/v, for acetic acid is about 0.14, 979). It must be remembered, of course, that...

With one exception, these results are based solely on quantum-chemical calculations of the potential energy surface. Theoretical evaluation of the transfer dynamics has been attempted only for the formic acid dimer, for which two general level splittings have been observed and assigned to synchronous double proton tunneling in the ground state and a vibrational excited state, respectively. 

An elegant example of the combination of infrared studies with kinetic and thermodynamic data to determine the overall mechanism of a catalytic reaction is the catalytic decomposition of formic acid. Its decomposition on silica-supported nickel has been investigated by several groups namely, Fahrenfort and co-workers (17, 69), Clarke and Pullin (70) and Hirota, Kuwata, and Nakai (71). Fahrenfort and Coworkers identified the prominent bands at 1575 and 1360 cm-1 as typical of carboxylate ions by comparison with the spectrum of nickel formate. These bands were assigned to the symmetrical and asymmetrical vibration of the O-C-O group, respectively. They showed that these bands were absent in the spectrum of formic acid adsorbed on the support. The formation of carboxylate ion (1575 cm-1 band) at room temperature was faster than the response time of the instrument, which was about 10 sec. The proposed mechanism is ... 

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