Experimental and theoretical vibrational study and the structure of CF3CO2CH2CF3 from gas-phase electron diffraction data and quantum chemical calculations

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

Opatija, Croacia

Congreso; EUCMOS 2008; 2008

Experimental and theoretical vibrational study and the structure of CF3CO2CH2CF3 from gas-phase electron diffraction data and quantum chemical calculations M. E. Defonsi Lestarda , M. E. Tuttolomdoa , E. L Varettib,1 , D. A. Wannc, H. E. Robertsonc ,  D. W. H. Rankinc and A. Ben Altabef a,*,1 a Instituto de Química Física, Facultad de Bioquímica, Química y Farmacia, Universidad Nacional de Tucumán, San Lorenzo 456, 4000 Tucumán, R.  Argentina. E-mail:altabef@fbqf.unt.edu.ar b Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, C. Correo 962, 1900 La Plata, R. Argentina cSchool of Chemistry, University of Edinburgh, West Mains Road, Edinburgh, UK EH9 3JJ.West Mains Road, Edinburgh, UK EH9 3JJ. West Mains Road, Edinburgh, UK EH9 3JJ. E-mail: d.w.h.rankin@ed.ac.uk   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 (HF, MP2) and DFT calculations using 6-31G(d), 6-311++G(d,p) and 6-311G(3df,3pd) basis sets1. Both experimental and theoretical data indicate that although both trans and gauche conformers are possible by rotating about the O-C bond, the preferred conformation is trans. To achieve this, two different schemes, i.e. the total energy and the natural bond orbital (NBO) partition schemes have been tried out. In addition, the total potential energy has been deconvoluted by a six-fold decomposition in terms of a Fourier-type expansion. Furthermore, the infrared spectra of 2, 2, 2- trifluoroethyl trifluoroacetate, CF3CO2CH2CF3, were obtained in the gaseous, liquid and solid states as well as the Raman spectrum liquid, The IR and Raman spectra unambiguously demonstrates the presence of trans and gauche geometries by the resolution of the most fundamentals modes  . The harmonic vibrational wavenumbers and the force field were calculated2. A set of scale factors calculated by a least square procedure, led to a final root mean square deviation (RMSD) of 10.17 cm-1. Figure 2. Calculated (upside) and experimental infrared spectra (liquid in the middle side and solid and gas in the downside) of CF3CO2CH2CF3 between 1050 and 600 cm-1. The calculated spectrum is obtained from B3LYP/6-311++G** frequencies and intensities using Lorentzian band shapes and populations for both conformers. Figure 1 Molecular structure, including numbering         scheme, for (a) conformer gauche, and (b) conformer trans of CF3CO2CH2CF3 [1] Gaussian 03, Revision B.02, Gaussian, Inc., Pittsburgh PA, 2003. [2]  P. Pulay, G. Fogarasi, G. Pongor, J. E. Boggs, A. Vargha, J. Am. Chem. Soc., 105 (1983) 7037