STRUCTURAL AND CONFORMATIONAL PROPERTIES OF 1,1,2,2-TETRAFLUOROETHYL METHYL-ETHER AS STUDIED BY MICROWAVE SPECTROSCOPY AND QUANTUM-CHEMICALCALCULATIONS

The microwave spectrum of 1,1,2,2-tetrafluoroethyl methyl ether (HCF2C F2OCH3) has been investigated in the 17.0-40.0 GHz spectral region at dry-ice temperature (-79 degrees C). Five all-staggered rotameric form s are possible for this compound. The gas phase consists of an equilib rium mixture, in which two rotamers, denoted Conformer I and Conformer III, could be observed through their rotational spectra. The latter r otamer was found to be the most stable form of the molecule, being 0.8 (4) kJ mol(-1) more stable than Conformer I. The ground vibrational st ale and five vibrationally excited states belonging to three different normal modes were assigned for III, while only the ground vibrational slate was assigned for I. The microwave work has been assisted by ab initio computations at the MP2/6-311++G* (frozen core) level of theor y, as well as density theory calculations at the B3LYP/6-31G level. T he structures and relative energies of the five conformers predicted i n both these computational schemes are rather close to one another. Ve ry good agreement with the experimental findings was found for rotamer s I and III.