The IR spectrum of methyl thioglycolate (MTG) was studied in three different phases, and interpreted with the aid of DFT calculations. The gas phase IR spectrum was explainable by the presence of the most stable conformer (syn-gauche-(-)gauche) only, while the IR spectrum of the liquid reveals strong intermolecular interactions, coincident with the formation of a dimeric form. The matrix-isolated spectra allow the identification of the second conformer (syn-gauche-gauche), in addition to the most stable form. The MTG dimer was also isolated by increasing the proportion of MTG in the matrix. The theoretical most stable structure of the dimer, which calculated IR spectrum agrees very well with the experimental one, is stabilized by a double interaction of the lone pair of the O atom of each of the C]O groups with the antibonding orbitals s* (SeH).

Dimethyl dithiodiglycolate (DTG), [CH 3 OC(O)CH 2 S] 2 , was synthetized by complete oxidation of methyl thioglycolate (MTG) with I 2 , and characterized by gas chromatography coupled with electron-impact mass spectrometry. Fifteen stable conformers were found with the B3LYP/6-31+G* approximation, with calculated populations at ambient temperature higher than 1 %. The IR and Raman spectra of liquid DTG were interpreted for the first time, in terms of equilibrium between four conformers. The UV-visible spectra of DTG in solutions of ethanol, isopropanol and acetonitrile present a low-intensity band around 230 nm, interpreted mainly as arising from n → π* transitions localized at the C=O groups, according to the prediction of TD-DFT calculations.

The photochemistry of methyl thioglycolate (MTG), CH 3 OC(O)CH 2 SH, in gas phase and in matrix isolation conditions was studied by means of FTIR spectroscopy, and the influence of the presence of molecular oxygen on the photochemical mechanisms was investigated. The UV-vis broad-band photolysis of MTG in gas phase originates CH 3 OC(O)CH 3 and S 8 , while in matrix conditions the photoproducts are CH 3 OH, H 2 CS, and CO, interacting inside the matrix cage. The photolysis of MTG in the presence of O 2 conducts to the formation of SO 2 , independent of the experimental conditions, being CH 3 OH, HC(O)OH, and CO the other photoproducts for the gas-phase photolysis, and H 2 CO, CH 4 , and CO 2 for the experiments performed in Ar matrix conditions.