The vibrational frequencies, normal modes of vibration, and force constants of CF3COF and CF3COCl are calculated using the MP2/6-31G(d＇) method. Our calculations agree with those of Pacansky ct al, in showing that the values of the nu(6), nu(7), nu(8), nu(12), and nu(13) experimental frequencies of CF3COF need to be reassigned. Our calculations also show that the same experimental frequencies in CF3COCl need to be reassigned. The calculated force constants are improved by fitting them to the reassigned experimental vibrations. The simple descriptions of vibrational motion previously given are shown to be inaccurate for most vibrations.