Use of G4 Theory for the Assessment of Inaccuracies in Experimental Enthalpies of Formation of Aromatic Nitro Compounds

Abstract

The gas-phase enthalpies of formation (Δ f H 298 °) of 101 aromatic nitro compounds were calculated using the Gaussian-4 (G4) theory applied to the atomization and isodesmic reaction energies. The Δ f H 298 °(g) values calculated from the atomization reactions were underestimated by an average of 13 kJ•mol −1 and they could not be used for the assessment of inaccuracies in the experimental enthalpies of formation. A good agreement with the most available experimental data was obtained using the isodesmic reaction procedure. From 5 to 26 isodesmic reactions with different reference species were constructed for each compound. About 15 aliphatic nitro compounds and 100 different C/H/N/O/Cl compounds were used as the reference species in these reactions; the accuracy of enthalpies of formation of all reference compounds was preliminarily confirmed by theoretical calculations. Evidence of accuracy of experimental data was provided by the agreement with calculated values. The differences between the calculated and the experimental enthalpies of formation in the range from (8 to 46) kJ•mol −1 were assigned to possible errors in the experimental values for 21 compounds. The theoretical Δ f H 298 °(g) values were recommended for these compounds as being more reliable than the experimental values. On the basis of theoretical results, a reference data set of internally consistent gas-phase enthalpies of formation of aromatic nitro compounds was provided. Both experimental and calculated values are included in this data set. The recommended Δ f H 298 °(g) values of aromatic nitro compounds are consistent with each other and with Δ f H 298 °(g) values of about 115 different C/H/N/O/Cl compounds including aliphatic nitro compounds. More accurate condensed phase enthalpies of formation and enthalpies of sublimation (or vaporization) were recommended in some cases based on a critical analysis of reported experimental data supplemented by quantum chemical calculations.

Accurate Thermochemistry of Novel Energetic Fused Tricyclic 1,2,3,4-Tetrazine Nitro Derivatives from Local Coupled Cluster Methods

“…The theoretical results are consistent with each other and the most reliable experimental values within 1 kcal mol −1 . In agreement with the general trends, 27,30,32,33 the differences between G4 and experimental values become more pronounced in the case of nitrobenzene 10 and dinitro derivatives of benzene 11 and 12 (Table 1). For example, in the case of the ortho arrangement of nitrogroups (11), G4 underestimates the formation enthalpy by ∼5 kcal mol −1 .…”

“…Therefore, we started with a thorough benchmark of the more demanding W1, W1-F12, and W2-F12 procedures along with the more affordable computationally G4 technique, which is widely employed for the species comprised of 20−30 non-H atoms. 32,33,58 To this end, we considered a number of simple nitro derivatives of the aromatic hydrocarbon and heterocyclic species (Chart 2) along with the smaller fused species 1−4 (Chart 1). The results are given in Table 1.…”

“…The gas phase enthalpies of formation (at p 0 = 1 bar and T = 298.15 K, Δ f H gas 0 ) were calculated using the explicitly correlated W1-F12 and W2-F12 multilevel procedures and atomization energy and isodesmic reaction approaches described in detail elsewhere. ,, As a general rule, the explicitly correlated F12 procedure remarkably accelerates the slow basis set convergence of conventional CCSD­(T) techniques . Note that the W1-F12 and W2-F12 procedures employed in the present work had been slightly modified in comparison with the originally proposed technique: namely, the B3LYP-D3BJ/def2-TZVPP optimized geometries (the ZPE correction factor of 0.99) were used , and the diagonal Born–Oppenheimer corrections were omitted.…”

Atom Pair Contribution Method: Fast and General Procedure To Predict Molecular Formation Enthalpies

“…The present data were taken from previous compilations, including the NIST Chemistry WebBook, 63 from which most of the values come; recent compilations of data for hydrocarbons, 4 CHO compounds, 64 and refrigerants; 65 and carefully curated data sets for nitroaromatic compounds (NACs), 66 azides, 67 aliphatic nitro compounds, and nitramines. 68 Additional data were also retrieved from original research papers, as detailed in the full database provided in the Supporting Information.…”

A facile approach to synthesize CdS–attapulgite as a photocatalyst for reduction reactions in water

“…Hence, it is urgent to enrich advanced materials and develop versatile technologies for environmental remediation. 3,32,33 As a chalcogenide photocatalyst, CdS has attracted much interest because of its narrow band gap, high light harvesting and excellent catalytic properties. [34][35][36] However, the limitations of the high recombination rate of photogenerated electron-hole pairs, photocorrosion problems, and easy agglomeration of CdS hinder its further application in photocatalysis.…”