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

Abstract

KEYWORDSTautomerization 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 2,4dioxo, 2-thio-4-oxo, 4-thio-2-oxo and 2,4-dithio derivatives of the deprotonated 5methylhydantoin 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 5methylhydantoin-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). DFT B3LYP Acidity Deprotonation Tautomerization 5-Methylhydantoin

Tautomeric Study of Neutral, Protonated and Deprotonated Isorhodanine Based on High Level Density Functional Theory

“…The calculations predict that the oxo/thione form (R1) is 5.2 kcal mol -1 more stable than the oxo/thiol form R4. These results are in agreement with the previous results, [5][6][7][8]27,28 The protonated and deprotonated oxo/ thione forms P2b and D1 are thermodynamically more stable than the protonated and deprotonated oxo/thiol forms P4a and D3 by 2.5 and 4.6 kcal mol Our results show that the neutral oxo/thiol forms R4 and R5 are more stable other neutral enol/thione and enol/thiol forms; implying that the hydrogen atom during the 1,3-H transfer process prefers to migrate to heteroatom of the thiocarbonyl group (C2=S7) than that of the other heteroatom of the carbonyl group (C2=O6). These results can be explained in terms of the higher polarizability and consequently the size of the sulfur atom than of the oxygen atom.…”

“…Great progress has been made in experimental and theoretical investigations of the protonation and deprotonation of heterocyclic compounds. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] Most of these studies have been carried out to predict the correct protonation and deprotonation sites and the possible role played by the protonation and deprotonation process in the isomerization process.…”

One-Pot Synthesis, Pharmacological Evaluation, Docking Study, and DFT Calculations for Selected Imidazolidine-2,4-Diones

“…There is aliphatic carbon and sulfur atom presence on the stereogenic centre for compound 2. Based on the previous study for hydantoin derivatives, (Zaki S Safi et al, 2018;Zaki Sulieman Safi, 2012) there are several tautomeric forms could exist for imidazolidine-2,4-dione as shown in Scheme 4.…”