European Journal of Chemistry

Theoretical density functional study of gas-phase tautomerization and acidity of 5-methylhydantoin and its thio derivatives

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Zaki Sulieman Safi


Tautomerization and acidities of various 5-methylhydantoins and their thio derivatives were predicted using Density Functional Theory (DFT). The functional used was B3LYP and the basis set for all atoms was 6-311+(d,p). Single point energy computations were performed at the 6-311+G(2df,2p) basis set. The relative stabilities of the different tautomers of the 2,4-dioxo, 2-thio-4-oxo, 4-thio-2-oxo and 2,4-dithio derivatives of the deprotonated 5-methylhydantoin have been studied. In all cases, the most stable deprotonated conformers are the oxo-thione, the dioxo or the dithio. As for the neutral and the protonated 5-methylhydantoin-thio derivatives, the tautomerization activation barriers are high enough as to conclude that the oxo-thione structures should be found in the gas phase. It was revealed that the ring-nitrogen atom at position 3 (N3) is more acidic than that at position 1 (N1), hence 5-methylhydantoin thio derivatives in the gas phase are an N3-acid. It has been found that the 2,4-dithio species is the most acidic compound among all the investigated compounds. The acidity values were found to be 343 (2O4O), 337 (2S4O), 336 (2O4S) and 332 kcal/mol (2S4S).


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Safi, Z. S. Theoretical Density Functional Study of Gas-Phase Tautomerization and Acidity of 5-Methylhydantoin and Its Thio Derivatives. Eur. J. Chem. 2012, 3, 348-355.

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