Experimental and computational study of the energetics of hydantoin and 2-thiohydantoin

Abstract

The standard (p°= 0.1 MPa) molar energies of combustion of hydantoin and 2-thiohydantoin were measured by static and rotating bomb combustion calorimetry, respectively. The standard molar enthalpies of sublimation, at T = 298.15 K, were derived from the temperature dependence of the vapour pressures of these compounds, measured by the Knudsen-effusion technique, and from high temperature Calvet microcalorimetry. The conjugation of these experimental results enables the calculation of the standard molar enthalpies of formation in the gaseous state, at T = 298.15 K, which are discussed in terms of structural contributions.We have also estimated the gas-phase enthalpy of formation from high-level ab initio molecular orbital calculations at the G3MP2B3 level of theory, being the computed values in good agreement with the experimental ones. Furthermore, this composite approach was also used to obtain information about the gas-phase basicities, proton and electron affinities and adiabatic ionization enthalpies.

Gas-phase basicities of polyfunctional molecules. Part 4: Carbonyl groups as basic sites

“…The two conformers resulting from protonation at the urea carbonyl, HYH , are of identical stabilities and a proton affinity value of 828 kJ/mol is calculated. The difference observed between this estimate and the previously published value of 821.7 kJ/mol (Silva et al, ) probably arise from the missing of the proton enthalpy in the PA calculation by Silva et al Protonation at the second carbonyl oxygen leads to a structure 19 kJ/mol less stable than HYH (G4MP2 result). Again, PA( HY ) may be compared to the value determined for N , N ‐dimethyl urea (903 kJ/mol, Scheme ).…”

“…Recently, proton affinities for the four possible protonations sites of hydantoin HY were calculated at the G3MP2B3 level of theory (Silva et al, ) (Scheme ). The urea carbonyl is found to be the most basic site and a PA( HY ) value of 821.7 kJ/mol has been proposed.…”

Energies of combustion and enthalpies of formation of 5-methyl-5-phenylhydantoin and 5,5-diphenylhydantoin

“…Despite the study made by Ribeiro da Silva et al [6][7][8] for hydantoin compounds, thermochemical data for the compounds under study in the present work were not found. Thus, the aim of this paper is to contribute to the knowledge of the thermodynamic and thermochemical properties of 5m5p and 5,5p.…”

“…The value obtained for hydantoin was 116.1 kJ mol -1 . From this value and the reported [8] enthalpy of formation in condensed phase, which is -(448.6 ± 1.1) kJ mol -1 , the enthalpy of formation in the gas phase was obtained as -332.5 kJ mol -1 . These results agree satisfactorily with the experimental values of (116.3 ± 0.7) and -(323.3 ± 1.3) kJ mol -1 , respectively [8].…”

An interpretation of the phenol nitration mechanism in the gas phase using G3(MP2)//B3-CEP theory

“…The G3 theory [28] and computationally less expensive versions of it, such as G3(MP2) [29] and G3(MP2)//B3 [30], are quantum mechanical methods that have been widely used in the study of a variety of compounds [31][32][33][34], rotational barriers [35,36], and mechanisms [37][38][39]. However, the size of molecular systems continues to be a limiting factor that prevents the more general use of Gaussian-n theories.…”