Structural and conformational properties of two sulfenyl derivatives, trifluoromethanesulfenyl acetate, CF3S-OC(O)CH3 (1), and trifluoromethanesulfenyl trifluoroacetate, CF3S-OC(O)CF3 (2), were determined by gas electron diffraction, vibrational spectroscopy, in particular with IR (matrix) spectroscopy, which includes photochemical studies, and by quantum chemical calculations. Both compounds exist in the gas phase as a mixture of two conformers, with the prevailing component possessing a gauche structure around the S-O bond. The minor form, 15(5)% in 1 and 11(5)% in 2 according to IR(matrix) spectra, possesses an unexpected trans structure around the S-O bond. The C=O bond of the acetyl group is oriented syn with respect to the S-O bond in both conformers. UV-visible broad band irradiation of 1 and 2 isolated in inert gas matrixes causes various changes to occur. Conformational randomization clearly takes place in 2 with simultaneous formation of CF3SCF3. For 1 the only reaction channel detected leads to the formation of CH3SCF3 with the consequent extrusion of CO2. Quantum chemical calculations (B3LYP/6-31G and MP2 with 6-31G and 6-311G(2df,pd) basis sets) confirm the existence of a stable trans conformer. The calculations reproduce the conformational properties for both compounds qualitatively correct with the exception of the B3LYP method for compound 2 which predicts the trans form to be prevailing, in contrast to the experiment.

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The gas-phase structures of tert-butyl vinyl ether, t-BuOC(H)CH2 (t-BVE), and (Z)-methyl 1-propenyl ether, MeOC(H)C(H)Me (Z-MPE), have been studied by gas electron diffraction and ab initio calculations (HF/3-21G and MP2/6-31G*). For both compounds only a single conformer with a slightly nonplanar anti structure of the CC−O−C skeleton was observed. The vibrationally averaged dihedral angles φ(CC−O−C) are 167(5)° (t-BVE) and 161(5)° (Z-MPE), respectively. The experimental scattering intensities are fitted slightly better with dynamic models and double minimum potentials for the internal rotation around the O−C(sp2) bonds. The dihedral angles of the equilibrium structures φe(CC−O−C) are 170(5)° for t-BVE and 161(8)° for Z-MPE. The potential barriers at the exactly planar anti conformation (φ(CC−O−C)=180°) are V 0 = 0.15(10) and 0.20(10) kcal mol-1, respectively. The experimental results are reproduced very well by MP2/6-31G* calculations (φe = 169.0° and 154.2° and V 0 = 0.12 and 0.11 kcal mol-1 for t-BVE and Z-MPE, respectively). The HF/3-21G method, however, predicts a planar structure (φe= 180°) for t-BVE and an anticlinal structure (φe = 138.7°) for Z-MPE.