Molecular structure and infrared spectra of dimethyl fumarate

Abstract

Infrared spectra of dimethyl fumarate isolated in low-temperature argon and xenon matrixes and of the compound in the solid amorphous and crystalline states have been studied. Theoretical calculations, carried out at the MP2/6-31G** and DFT(B3LYP)/6-31G** levels, predict three planar conformers of low internal energy, all of them exhibiting the methyl ester moieties in the cis(C–O) configuration: the conformational ground state (conformer I), with the two OC–CC dihedrals equal to 0°, and forms II and III, where one or both OC–CC dihedrals are 180°. In the spectra of the matrix isolated compound, characteristic bands of all three conformers were identified. During annealing of the xenon matrix up to 60 K, conversion of the less stable conformers, II and III, into the most stable conformer, I, was observed. In the amorphous solid, these three conformers could also be identified spectroscopically. The IR and Raman spectra of the crystalline phase clearly show that in the crystal only form I is present, since no bands ascribable to other conformers could be observed.