Molecular structure and infrared spectra of dimethyl oxalate

Abstract

Infrared spectra of dimethyl oxalate isolated in low-temperature argon matrix and of the compound in the solid amorphous and crystalline state are reported. The experimental observations are interpreted in terms of a large amplitude, low frequency vibration along the torsional coordinate OC–CO. Assumption of the large amplitude vibration allows consistent explanation of the spectra observed in matrixes and in the gas phase, and the differences between these and the spectrum of the compound in the crystalline state, in which the planar trans structure is fixed. IR spectra of crystalline dimethyl oxalate clearly show that in the relaxed crystal lattice only the trans form is populated. Davydov splitting, due to the presence of two molecules per unit cell, was observed for several bands in the IR spectrum of the crystalline compound.