Vinyl formate in the gas phase, investigated by electron diffraction, microwave spectroscopy and infrared band contour analysis, supplemented with molecular mechanics and ab-initio calculations of geometries and force fields

Abstract

The structure of vinyl formate was studied by joint analysis of gas phase electron diffraction, microwave and infrared data including band profiles. The experimental data were supplemented with vibrational constraints taken from force field calculations on the 4–21G ab initio level, and with geometrical constraints arising from molecular mechanics (MM2 force field), STO-3G and geometry-relaxed 4–21G ab initio calculations. All data are in accord with a planar heavy-atom skeleton in the ( sp, ap) conformation, i.e. torsion angle φ(OCOC) = 0° and φ(CCOC) = 180°. From the occurrence of a single form at room temperature, it follows that ( sp, ap) is at least 2.3 kcal mol −1 more stable than the next conformer. Geometry constrained models based on MM2 and the STO-3G constraints were rejected on statistical grounds. The analysis favours the 4–21G constrained models. Subject to the ab initio constraints, the following internal coordinates ( r g -distances, r 0 α-angles) were found: CC, 1.331 Å; (C)CO, 1.397 Å; (O)CO, 1.350 Å; CO, 1.193 Å; CH, 1.087 Å; CCO, 121.0°: COC, 117.0°; OCO 127.2°.