Ab initio study of the potential energy well of dithiomalondialdehyde on varying the S⋯S distance

Abstract The potential energy well evolution on varying the S⋯S distance of the intramolecular S–H⋯S hydrogen bridge of dithiomalondialdehyde and the related frequencies of the S–H stretching vibration mode were calculated at different levels of ab initio calculations. The trend of the curves, as well as that of the proton transfer barrier, are similar to those of malondialdehyde, which was previously studied. The limit distance for passing from double to single minima is 3.15–3.2 A. The very low hydrogen bond energy ( E HB ) undergoes remarkable changes on changing the approach adopted for the correlation energy calculation (MP2 or B3LYP) and on the zero point energy correction. To test its dependence on the conjugation and steric effects, calculations were extended also to 3-formyl-dithiomalondialdehyde, 3- t -butyl-dithiomalondialdehyde, dithioacetylacetone and 3- t -butyl-dithioacetylacetone. Unlike in malondialdehyde and acetylacetone, cumbersome groups in the 3 position cause weakening or complete breaking of the hydrogen bridge.