Multireaction Approach to Quantum Thermochemistry

Abstract

Gas-phase enthalpies of formation are frequently obtained from electronic-structure calculations. For a compound containing elements that are not permanent gases, experimental data are needed to connect the ab initio energies with the elements in their standard states. Usually only one chemical reaction, such as atomization, is used to make this connection. Using a single reaction has the supposed advantage of producing a single value, but it remains challenging to estimate the associated uncertainty. Here, we propose using several chemical reactions instead of one. This yields several values for the target enthalpy of formation. The relative reliability of each reaction is estimated and used for weighted averaging of the corresponding enthalpies of formation. The resulting weighted mean is an estimate for the target quantity, and the standard deviation of the weighted mean is a reasonable estimate for the associated standard uncertainty. Two implementations are explored here and applied predictively to dihydrolevoglucosenone (cyrene), which has been proposed as a "green" polar aprotic solvent.

Commodity Chemicals and Fuels from Biomass: Thermodynamic Properties of Levoglucosan Derivatives

“…An extended computational study of Cyrene by the highlevel coupled-cluster CCSD(T)-F12b method has been published just recently. 52 The average of 11 isodesmic reaction values of Δ f H m o (g, 298.15 K) theor = −435.7 ± 5.0 kJ•mol −1 for Cyrene is in good agreement with our theoretical and experimental results (Table 11).…”

The Corrected Values of ΔrHo(CaHbOd, a≤16) of Atomization of the Aromatic Compounds and Their Uncertainties Determined Using Several Quantum Mechanical Approaches

“…The most reliable values of Δ f H o (X n , TAB) of 28 compounds (SI, Note 1) are boldfaced. The reference values of Δ r H o (X n , TAB) of atomization of the considered 28 compounds X n , calculated using the most reliable values of Δ f H o (X n , TAB) and the literature values of Δ f H o (H, 3 C and 3 O, TAB), [10] are also presented in SI, Note 1.…”

“…The simplest and most universal way for the increasing accuracy of determination of Δ f H o 298.15 (X) of large compounds is using the thermochemistry of homodesmotic and isodesmic reactions, [1] or other schemes capable to eliminate the systematic errors of their calculations. [2][3][4] However, these approaches are limited by the accuracy of the measured (or literature) values of Δ f H o 298.15 of compounds, used for these reactions or schemes, as well as they are requiring the additional calculations of thermochemical properties of others components of reactions. These schemes are based on the thermochemistry of reactions included several components, thermochemical properties of only one of which are unknown.…”