The structure of trimethoxymethane in the gas phase,an electron diffraction,ab initio and molecular mechanics study

The structure of trimethoxymethane in the gas phase was studied by electron diffraction, ab initio molecular orbital calculations and molecular mechanics. The molecule was found to exist almost exclusively as an asymmetric all-staggered TGG conformer. The electron diffraction structural parameters (r_g distances, r_α angles) as obtained from geometrically consistent r_α-refinements are: r(C-O) central 1.382(6) Å, r(C-O) terminal 1.418(6) Å, r(C-H) 1.112(1) Å, ∠(O-C-O) in the gauche—gauche chain 115.0(1.0)°, in the gauche-anti chains 109.2(0.6)° ∠(C-O-C) 114.3(0.6)°, ∠(O-C-H)_Me 109.9(0.3)°, methyl torsion 68(6)°. The structure is adequately reproduced by molecular mechanics calculations applying Allinger's force field. The structures of methoxymethanes can be explained in terms of the anomeric effect. This is confirmed by ab initio calculations.