Gas-phase structure and new vibrational study of methyl trifluoroacetate (CF3C(O)OCH3)

Abstract

The molecular structure of methyl trifluoroacetate (CF3C(O)OCH3) has been determined in the gas phase from electrondiffraction data supplemented by abinitio (MP2) and DFT calculations using different basis sets. Experimental data revealed an anti conformation with a dihedral angle θ (CCOC) = 180°. Quantum mechanical calculations indicate the possible existence of two conformers, differing by a rotation about the C(O)-O bond. The global minimum represents a Cs-symmetric structure in which the CF3 group has the anti orientation with respect to the CH3 group,but there is another potential minimum, much higher in energy, representing a Cs-symmetric structure with a cis conformation. The preference for the anti conformation was studied using the total energy scheme and the natural bond orbital (NBO) partition scheme. Additionally, the total potential energy has been deconvoluted using a six-fold decomposition in terms of a Fourier-type expansion, showing that the electrostatic and steric contributions are dominant in stabilizing the anti conformer. Infrared spectra of CF3C(O)OCH3 were obtained for the gaseous and liquid phases, while the Raman spectrum was recorded for the liquid phase. Harmonic vibrational frequencies and a scaled force field have been calculated, leading to a final root mean-square deviation of 9cm-1 when comparing experimental and calculated frequencies. © 2009 John Wiley & Sons, Ltd.