Water-assisted proton transfer in formamide, thioformamide and selenoformamide

Abstract

The tautomeric equilibria of formamide, thioformamide and selenoformamide were studied in the gas phase and in water solution using ab initio quantum chemical calculations. The solvent effects were considered by explicit inclusion of three water molecules, which model a first hydration shell around the solute. Full geometry optimizations of these complexes were carried out at MP2/6-31G(d,p) and MP2/6-31+G(d) levels of theory. Single point calculations were performed at MP4/6-31+G(d)//MP2/6-31+G(d) computational level to obtain more accurate energies. The basis set and electron correlation effects on the energy barriers of tautomerization and the energy differences between tautomers were analyzed. The minimum energy paths for water-assisted proton transfer in tri-hydrated formamide and its chalcogen analogues thioformamide and selenoformamide were followed at MP2/6-31+G(d) level.