Structural and thermochemical properties of methyl ethyl sulfide alcohols: HOCH2 SCH2 CH3 , CH3 SCH(OH)CH3 , CH3 SCH2 CH2 OH, and radicals corresponding to loss of H atom

Probing the Chemistry of Sulfurous Pollutants: Accurate Thermochemistry Determination of Extensive Sulfur-Containing Species

Sulfur-containing fuels, such as petroleum fuels, natural gas, and biofuels, produce SO2, SO3, and other highly toxic gases upon combustion, which are harmful to human health and the environment, making it essential to understand their thermochemical properties. This study used high-level quantum chemistry calculations to determine thermodynamic parameters, including entropy, enthalpy, and specific heat capacity for an extensive set of sulfur-containing species. The B3LYP/cc-pVTZ level of theory was used for geometry optimization, vibration frequency, and dihedral scan calculations. To determine an appropriate ab initio method for energy calculation, the Bland-Altman diagram, a statistical analysis method, was employed to visualize the 298 K enthalpy value between experimental data and three sets of ab initio methods: G3, CBS-QB3, and the average of G3 plus CBS-QB3. The CBS-QB3 method exhibited the highest accuracy and was eventually selected for the energy calculation in this study. Thermochemical property parameters were then calculated with the MultiWell program suite for all these sulfur-containing species, and the results were in good agreement with the thermochemical data of organic compounds and the National Institute of Standards and Technology Chemistry WebBook databases. The thermochemical property database established in this study is essential to studying sulfur-containing species in desulfurization.

Heat Capacity Estimation Using a Complete Set of Homodesmotic Reactions for Organic Compounds

Reliable information about isobaric heat capacities C_P is necessary to determine the energies of organic compounds and chemical processes at an arbitrary temperature. In this work, the possibility of theoretical estimation of C_P by the homodesmotic method is analyzed. Three cases of C_P calculation applying the methodology of the complete set of homodesmotic reactions (CS HDRs) are considered: the gas- and liquid-phase C_P of organic compounds of various classes at 298 K (the mean absolute value of reaction heat capacity, MA ΔC_P = 1.44 and 2.83 J/mol·K for the gas and liquid phase, correspondingly); and the gas-phase C_P of n-alkanes C₂-C₁₀ in the temperature range of 200-1500 K with an average error in calculating the heat capacity of 0.93 J/mol·K. In the latter case, the coefficients of the Shomate equation are determined for all n-alkanes that satisfy the homodesmoticity condition. New values of gas- and liquid-phase heat capacities are obtained for 41 compounds. The CS HDRs-based approach for estimating the C_P of organic compounds is characterized by high accuracy, which is not inferior to that of the best C_P-additive schemes and allows us to analyze the reproducibility of the calculation results and eliminate unreliable reference data.