We present the synthesis and structure determination for two thiohydantoin compounds (5-benzylidene-2-sulfanylideneimidazolidin-4-one and 5-cinnamylidene-2-sulfanylideneimidazolidin-4-one), proposed as potential novel fungicides. The exact chemical structure of these molecules has not yet been determined since they can potentially exist in several tautomeric and geometric forms (Z-E isomerism). The geometries of all the theoretically possible structures of the studied compounds were optimised. The calculations were performed at the density functional theory level using the B3LYP functional and the 6-311++G** basis set. Based on our calculations, the most probable structures of the studied compounds were proposed. The theoretical predictions were verified by comparing the calculated IR as well as the 1H and 13C NMR spectra with the experimental data. It was documented that both the studied compounds exist predominantly in the tautomeric structure, in which the movable hydrogen is connected to the nitrogen atom in the hydantoin ring. It has been experimentally proven that one of the studied compounds occurs only as a single structure, whereas the other one exists as a mixture of two geometric isomers. Schematic presentation of synthesis reaction and predicted percentage contents of studied compounds in products mixture.
Keywords: 2-thiohydantoin; Hydantoin; Structure determination; Tautomerism; Theoretical calculations.