GREMMLENZ UNICAMP

This study delves into the tautomeric equilibrium of the thione/thiol forms of 1,3-thiazolidine-2-thione through a comprehensive exploration using nuclear magnetic resonance, infrared, and ultraviolet–visible spectroscopies. The experimental findings are bolstered by density functional theory, shedding light on the predominance of the thione tautomer in the solid state—a consensus supported by previously reported crystallographic data.

In solution, the dynamic tautomeric equilibrium was scrutinized using 1H NMR across various temperatures in four deuterated solvents: acetonitrile, dimethylsulfoxide, chloroform, and methanol. The equilibrium constants (K = (thiol)/(thione)) and free Gibbs energies were derived by integrating N-bonded hydrogen signals at each temperature for each solvent, excluding methanol from the analysis. The endothermic tautomerization was found to be entropy-driven, and the combined influence of solvent and temperature provided a pathway to achieve nearly 50% thiol concentrations in solution.

Theoretical investigations into the electronic transitions were conducted, employing time-dependent DFT to assign bands and elucidate the impact of solvent on the energy of the spectra’s key bands.

Embark on a journey through theoretical and experimental realms to unravel the intricacies of the tautomeric equilibrium in 1,3-thiazolidine-2-thione.