STRUCTURAL AND CONFORMATIONAL-ANALYSIS OF DIETHYL-ETHER BY MOLECULAR-ORBITAL CONSTRAINED ELECTRON-DIFFRACTION COMBINED WITH MICROWAVE SPECTROSCOPIC DATA

The molecular structure and conformation of diethyl ether, C(3)H3C(2)H ,O(1)C(4)H2C(5)H-3, at 27 degrees C was studied by a joint analysis of gas electron diffraction and microwave spectroscopic data. Vibrationa l mean amplitudes and shrinkage corrections were calculated on the bas is of the vibrational spectra measured in the vapor and liquid phases. Ab initio geometry optimization at the HF/4-21G level was performed o n four possible conformers and the results were used as structural con straints. Diffraction and vibrational spectroscopic data are consisten t with the presence of two conformers, trans-trans (TT, dihedral angle s phi(1)(C4O1C2C3) = phi(2)(C2O1C4C5) = 180 degrees) and trans-gauche (TG), in the vapor phase. The compositions of the TT and TG conformers were determined to be 69(8) and 31%, respectively, by thejoint analys is. The structural parameters of the TT form determined are r(g)(O-C) = 1.419(1) Angstrom, r(g)(C-C) = 1.514(2) Angstrom, (r(g)(C-H)) = 1.11 4(2) Angstrom, angle(alpha)COC = 113.5(4)degrees, angle(alpha)OCC = 10 8.6(1)degrees, angle(alpha)OCH = 110.4(9)degrees, and (angle(alpha)CCH ) = 110.5(7)degrees, where values in parentheses are error estimates ( 3 sigma) and those in angle brackets denote average values. The struct ural differences between the TT and TG conformers were taken from the 4-21G calculations except for the dihedral angles of the TG form, whic h were determined to be phi(1) = 76(10)degrees and phi(2) = 161(15)deg rees.