Vibrational and ab initio conformational analysis of 2,2,2-trifluoroethyl formate

Infrared and Raman spectra (4000-50 cm(-1)) of gaseous, amorphous and crystalline solid 2,2,2-trifluoroethyl formate (TFEF), HCOOCH2CF3, have been recorded. DFT ab initio calculations were carried out using a 6-31G* basis set. The calculations show that the compound can occur as the s-cis,trans, the s-cis,gauche and the s-trans,gauche conformers. For each conformer the optimized structural parameters, the vibrational wavenumbers and infrared intensities were calculated. Both s-cis conformers were identified in the vibrational spectra of all fluid phases. In the crystalline solid only the s-cis,trans is present. No evidence for the presence of the s-trans,gauche conformer in the fluid phases was found. The enthalpy difference between the s-cis,gauche and s-cis,trans conformers in the liquid and the vapor phase were determined to be 2.8(11) and 2.8(13) kJ mol(-1), respectively. A complete assignment of the infrared and Raman spectra is proposed. (C) 2000 Elsevier Science B.V. All rights reserved.