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

The potential energy well evolution on varying the S ... S distance of the intramolecular S-H ... S hydrogen bridge of dithiomalondialdehyde and the r elated frequencies of the S-H stretching vibration mode were calculated at different levels of ab initio calculations. The trend of the curves, as wel l as that of the proton transfer barrier, are similar to those of malondial dehyde, which was previously studied. The limit distance for passing from d ouble to single minima is 3.15-3.2 Angstrom. The very low hydrogen bond ene rgy (E-HB) undergoes remarkable changes on changing the approach adopted fo r the correlation energy calculation (MP2 dr B3LYP) and on the zero point e nergy correction. To test its dependence on the conjugation and steric effe cts, calculations were extended also to 3-formyl-dithiomalondlialdehyde, 3- t-butyl-dithiomalondialdehyde, dithio-acetylacetone and 3-t-butyl-dithioace tylacetone. Unlike in malondialdehyde and acetylacetone, cumbersome groups in the 3 position cause weakening or complete breaking of the hydrogen brid ge. (C) 2000 Elsevier Science B.V. All rights reserved.