Stable Configuration of Methyl Groups in Dimethyl Ether

Abstract

THE internal rotation of a methyl group about its symmetry axis, despite the presence of the group in a great variety of organic molecules, has attracted little attention, probably because experimental methods such as dipole moment measurement, etc., are not available for the elucidation of the problem. In the structural determination of molecules containing methyl groups, each group is often considered as a whole rather than as four separate atoms¹. However, the determination is not complete, unless the stable configuration of hydrogen atoms in molecules is taken into account. Recent advances in the experimental technique of electron diffraction by gas molecules have made it possible to determine the values of structural parameters with higher precision than formerly. For the present purpose, a dimethyl ether molecule is perhaps the simplest prototype amenable to the sector-microphotometer method in electron diffraction, because the molecule has non-bonded C … H distances which are sensitive to the rotation of methyl groups and contribute appreciably to the total scattered intensity.