Experimental and theoretical studies of the vibrations and structure of 2,2,2-trifluoroethylacetate, CF3CO2CH2CF3

M. E. DEFONSI LESTARD; M. E. TUTTOLOMONDO; E. L. VARETTI; D. A. WANN; H. E. ROBERTSON; D. W. H. RANKIN; A. BEN ALTABEF

JOURNAL OF MOLECULAR STRUCTURE

ELSEVIER SCIENCE BV

Año: 2009 vol. 917 p. 183 - 192

0022-2860

   The molecular structure of 2,2,2-trifluoroethyl trifluoroacetate, CF3CO2CH2CF3, has been determined in the gas-phase from electron-diffraction data supplemented by ab initio (MP2) and DFT calculations using basis sets up to 6-311++G(d,p). Both experimental and theoretical data indicate that, although both structures with anti, anti (Cs) and anti, gauche (C1) conformations exist by rotating about the OAC(H2) bond, the anti, anti structure is preferred. The difference in free energy was calculated to be 2.1 kJ mol_1 (Cs conformer lower in energy) and as the C1 conformer has a double multiplicity relative to the Cs conformer, the ratio of C1–Cs conformer was predicted to be 0.41: 0.59. This conformational preference was studied using the total energy scheme and the natural bond orbital partition scheme. Additionally, the total potential energy has been deconvoluted using six-fold decomposition in terms of a Fourier-type expansion. Infrared spectra of CF3CO2CH2CF3 have been obtained for the gaseous, liquid and solid phases and the Raman spectrum for the liquid phase. Harmonic vibrational frequencies and a scaled force field have been calculated, leading to a final root-mean-square deviation of 7.3 cm_1.