Density Functional Computational Thermochemistry:  Isomerization of Sulfine and Its Enthalpy of Formation

Abstract

Density functional (DFT), second-order perturbation theory (MP2), and coupled-cluster [(CCSD(T)] calculations using Pople's basis sets up to 6-311++G(3df,2pd) and Dunning's correlation consistent basis sets have been employed to determine the enthalpy of formation of sulfine, CH2SO, 1, using the isodesmic reaction CH2S + SO2 ⇌ CH2SO + SO. Previous calculations showed an inconsistency between the enthalpy of formation obtained using this methodology, Δf H o 298.15(1) = −52 ± 10 kJ/mol, and the value obtained employing the isomerization reaction CH2SO (1) ⇌ HC(O)SH (2) if Benson's estimate for the enthalpy of formation of isomer 2 (thioformic acid) was employed. This result was particularly vexing, since the computed enthalpy of formation of 1 was reasonably in agreement with Benson's own estimate. In this paper we extended our previous study using the reactions HC(O)−XH + RH ⇌ H2CO + R−XH with R = H, Me, Et, Pr, and i-Pr. X was either sulfur, to obtain the enthalpy of formation of 2, or oxygen, to assess the errors to be expected in the use of these reactions for the evaluation of Δf H°. The result, Δf H o 298.15(2) = −121 ± 8 kJ/mol, arrived at after a critical assessment of B3LYP, MP2, and CCDSD(T) results, is in complete agreement with the value of −126 ± 4 kJ/mol estimated by Benson. This implies that the isomerization reaction cannot be employed for the determination of the enthalpy of formation of sulfine. We ascribe this inadequacy to the errors introduced due to the change in the oxidation state of sulfur.

High-Accuracy Theoretical Thermochemistry of Atmospherically Important Sulfur-Containing Molecules

“…The DFT results were also confirmed with calculations carried out with the CCSD(T) method, and finally, the values obtained at the B3PW91/ 6-311þþG(3df,2pd) and FC-CCSD(T)/6-311þþG(2df,2pd) levels of theory were averaged and accepted as Δ f H 298 °(CH 2 SO). In their second paper, 124 the previously calculated value of 52.0 ( 10.0 kJ/mol was confirmed on the basis of DFT, MP2, and CCSD(T) calculations with Dunning's correlation-consistent basis sets. In order to solve the discrepancy between Ruttink and associates' CBS-QB3 120 and their previous results, 123,124 Ventura and co-workers 125 performed DFT calculations on three additional reaction schemes not considered earlier.…”

“…In their second paper, 124 the previously calculated value of 52.0 ( 10.0 kJ/mol was confirmed on the basis of DFT, MP2, and CCSD(T) calculations with Dunning's correlation-consistent basis sets. In order to solve the discrepancy between Ruttink and associates' CBS-QB3 120 and their previous results, 123,124 Ventura and co-workers 125 performed DFT calculations on three additional reaction schemes not considered earlier. They concluded that the discrepancy is connected to the presence of the triplet SO in the isodesmic reaction (see above) used to calculate the heat of formation of sulfine.…”

Computer simulations and analysis of structural and energetic features of crystalline cage energetic compound: 2, 4, 6, 8, 12-pentanitro-10-(3, 5, 6-trinitro (2-pyridyl))-2, 4, 6, 8, 12-hexaazatetracyclo [5.5.0.03,11 .05,9 ]dodecane

“…The method of isodesmic reactions, in which the number of each kind of formal bond is conserved, has been employed very successfully to calculate HOF from total energies obtained from ab initio calculations . In order not to break the skeleton, we take CL‐20 and pyridine as a reference compound; the isodesmic reaction (1) used to derive the HOF of PNTNPHATCD is as follows:…”

The heats of formation in a series of nitroester energetic compounds: A theoretical study

“…Hence, various reports of the heats of formation of the molecules have been given by various isodesmic reaction schemes [15,[30][31][32][33][34]. Ventura et al [35,36] have pointed out that DFT methods using modest basis sets and isodesmic reactions can produce very accurate thermochemical information, in many cases superior to results from Gaussian-2 (G2) and even the coupled cluster method (CCSD(T)).…”