UV-visible,IR, and 13C NMR studies on CT complexes between some thiohydantoins and molecular diiodine

The reaction of some 5,5-dimethyl-2-thiohydantoin derivatives (X = O, S; R, R′ = H, Me) with molecular diiodine has been studied in CH₂Cl₂ solution by different spectroscopic techniques. The formation constants (K) of the 1 : 1 molecular adducts and their thermodynamic parameters have been measured by UV-visible spectroscopy. The results allow us to point out the different donor properties of C(2) = S thioketonic sulfur between the two series of compounds (X = O, S) and the influence of N(1) and N(3) methylation on the K's. From the analysis of the ν(NH) frequencies, it has been possible to show hydrogen bond interactions between the NH's and the S-bonded iodine; this seems to be an important factor in determining the K values.