The geometric structures and conformational properties of bis(fluoromethyl) ether, CH2FOCH2F, bis(difluoromethyl) ether, CHF2OCHF2, and pentafluoromethyl ether, CF3OCHF2, have been studied with gas electron diffraction and quantum chemical methods (B3LYP/6-31G* and MP2 with 6-31G*, cc-pVTZ or 6-311G(2df) basis sets). IR(matrix) spectra have been recorded for CF3OCHF2. The most stable [sc,sc] conformer of CH2FOCH2F possesses C-2 symmetry with the C-F bonds of both CH2F groups in synclinal (sc, counterclockwise) orientation (phi(C-O-C-F) = 70(2)degrees). A small contribution (less than or equal to14%) of the [sc,-sc] form with C, symmetry cannot be excluded (-sc = synclinal, clockwise). CHF2OCHF2,, exists in the gas phase as a mixture of two forms. In the main [ap,sp] conformer (82(8)%) one C-H bond is oriented antiperiplanar (ap), the other one synperiplanar (sp). This latter C-H bond nearly eclipses the opposite O-C bond with phi(C-O-C-H) = 18(2)degrees. Nearly eclipsed orientation of the C-H bond is also favored in CF3OCHF2, with phi(C-O-C-H) = 19(3)degrees. According to IR(matrix) spectra a small (8(3)%) contribution of the [ap] conformer with the C-H bond antiperiplanar relative to the opposite O-C bond is present at room temperture. The conformational properties of these fluorinated dimethyl ethers can be rationalized by orbital interaction energies derived from a natural bond orbital (NBO) analysis.