Microwave Spectra and Structure of Dimethyl Ether

Abstract

The microwave spectra of six isotopic species of dimethyl ether were investigated from 8–48 Gc. From the changes in moments of inertia with C13 and O18 substitutions the CO distance and <COC were found to be 1.410±0.003 Å and 111°43′±20′, respectively. The conformation of the methyl groups was determined from the (CH2D) (CH3)O species. Dimethyl ether has C2v symmetry and the methyl groups are staggered with respect to the opposite CO bonds. The data from deuterium substitutions could only be satisfactorily fit by a structure containing asymmetric methyl groups. The two CH distances in this structure differ by 0.009 Å, the < HCH by 49′, and the angle between the CO internuclear line and a perpendicular to its respective hydrogen plane is 2°31′±40′. If an average CH distance of 1.0956 Å is assumed the average <HCH is 109°29′. The structure of the asymmetric methyl groups is shown to be consistent with s and p hybridization of the carbon orbitals. In this scheme the carbons form ``bent bonds'' with the oxygen. From the Stark effect the dipole moment of dimethyl ether was determined to be 1.31±0.01×10—18 esu.