2,4-diselenouracil tautomers: structures, energies, and a comparison with uracil and 2,4-dithiouracil

Abstract

A first theoretical investigation of the structure and gas-phase tautomeric equilibria of 2,4-diselenouracil is presented. The molecular geometries of six diselenouracil tautomers were obtained at the MP2 level of theory with a basis set of DZP quality. Their relative energies were estimated up to the MP4(SDQ) level. After including the HF-level ZPE energy contributions, the energy difference between the two most stable tautomers is 8.1 kcal mol −1 at the MP4(SDQ) level. The third most stable tautomer is 9.0 kcal mol −1 less stable than the major tautomeric form. The ZPE contributions change the relative stability of the second and third most stable diselenouracil tautomers. Geometries, dipole moments, and relative tautomeric energies of 2,4-diselenouracil are very similar to those for 2,4-thiouracil.