Structural and conformational analysis of diethyl ether by molecular orbital constrained electron diffraction combined with microwave spectroscopic data

Abstract

The molecular structure and conformation of diethyl ether, C(3)H 3C(2)H 2O(1)C(4)H 2C(5)H 3, at 27°C was studied by a joint analysis of gas electron diffraction and microwave spectroscopic data. Vibrational mean amplitudes and shrinkage corrections were calculated on the basis of the vibrational spectra measured in the vapor and liquid phases. Ab initio geometry optimization at the HF/4-21G level was performed on four possible conformers and the results were used as structural constraints. Diffraction and vibrational spectroscopic data are consistent with the presence of two conformers, trans-trans (TT, dihedral angles φ 1(C 4O 1C 2C 3) = φ 2(C 2O 1C 4C 5) = 180°) 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 the joint analysis. The structural parameters of the TT form determined are r g(OC) = 1.419(1) Å, r g(CC) = 1.514(2) Å, 〈 r g(CH)〉 = 1.114(2) Å, ∠ αCOC = 113.5(4)°, ∠ αOCC = 108.6(1)°, ∠ αOCH = 110.4(9)°, and 〈∠ αCCH〉 = 110.5(7)°, where values in parentheses are error estimates (3σ) and those in angle brackets denote average values. The structural differences between the TT and TG conformers were taken from the 4-21G calculations except for the dihedral angles of the TG form, which were determined to be φ 1 = 76(10)° and φ 2 = 161(15)°.