Tautomeric Study of Neutral, Protonated and Deprotonated Isorhodanine Based On High Level Density Functional Theory

High level Density Functional Theory (DFT) using B3LYP/6-311++G(2df,2p)//6-311+G(d,p) calculations on the relative stabilities and structures of the neutral, protonated and deprotonated isorhodanine tautomeric forms are reported in the gas phase and solution. Gas phase and solution B3LYP calculations predict that the oxo/thione tautomer is the most stable one in all cases. Comparison of the gas phase results, bond lengths, bond angles and relative energies, with those of the solution reveals very strong linear relationships. Results of the calculated proton affinities (PAs), molecular gas phase basicity (GBs) and deprotonation enthalpies (DHdep) indicate that isorhodanine behaves as a sulfur base. The isomerization processes leading from the most stable species to the less stable ones are also investigated.