Hexafluoroacetone, HFA, has been used as a stabilizer for peptide structures, as protecting and activating reagent, and as a structure modifier in proteins. The vibrational spectra of HFA have been the subject of several studies [1-5]. Berney [1], based on the depolarization ratios of the Raman spectrum of HFA, concluded a Cs structure with two CF3 groups staggered with respect to each other. Berney also, by considering the optional vibration of the CF3 groups, estimated the barrier to rotation of the CF3 groups of about 1000 cm-1. Pace et al. [2] by assuming a C2v structure for HFA reassigned the vibrational spectra of HFA. These authors, based on the calorimetric measurements in the gas phase, predicted a barrier to rotation for the CF3 groups of about 1000-1500 cal/mol. Pertillä [3] by assuming a C2v structure and using normal coordinate analysis reconsidered the vibrational spectra of HFA. Durig et al. [5], by considering the far infrared spectrum of HFA, a barrier to rotation of 777±5 cm-1 and a Cs structure concluded. Campton et al. [4], by using an ab initio SCF calculation, reconsidered the vibrational spectra assignment of HFA. The symmetry obtained by the SCF calculation of Compton et al. [4] is consistent with the two electron diffraction results, which conclude a C2 symmetry for the HFA molecule [6,7]. The calculated energy difference between the C2V and C2 structures is 4.9 kJ/mol [4].

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