Gas-phase Standard Molar Enthalpies Research Articles

Thermochemistry of amino-1,2,4-triazole derivatives

AbstractThe present work is focused on determining the enthalpy of formation of several derivatives of amino-1,2,4-triazoles. Experimentally, the enthalpies of formation of the crystalline phase and the enthalpies of sublimation of 3-amino- and 3,5-diamino-1H-1,2,4-triazole were derived, respectively, from static-bomb combustion calorimetry and Calvet microcalorimetry or Knudsen effusion measurements. For 4-amino-4H-1,2,4-triazole, only the enthalpy of sublimation was measured. Gas-phase standard molar enthalpies of formation were also estimated using theoretical calculations performed with the G3(MP2) composite approach. The very good agreement of these estimates with the experimental results, support the extension of this study to the estimate of this property for the remaining compounds not studied experimentally. The results obtained are interpreted in terms of structural contributions.

A combined experimental and computational thermodynamic study of fluoronitrophenol isomers

Combustion energies of the 5-fluoro-2-nitrophenol, 4-fluoro-2-nitrophenol, 3-fluoro-4-nitrophenol and 2-fluoro-4-nitrophenol isomers were obtained by means of a rotating-bomb combustion calorimeter. From these determinations, standard molar combustion enthalpies and standard molar formation enthalpies, at T = 298.15 K, in the crystalline state, were derived. The Knudsen mass-loss effusion technique was used to determine the standard molar enthalpies, entropies and Gibbs energies of sublimation, at T = 298.15 K, of the studied compounds. The standard molar enthalpies of sublimation of the four isomers were also measured by Calvet microcalorimetry. The gas-phase standard molar enthalpies of formation were derived from the experimental measurements, at T = 298.15 K, for the fluoronitrophenols studied.Additionally, the standard molar enthalpies of formation were estimated by means of computational methodology at the G3(MP2)//B3LYP level. The estimated values are in very good agreement with experimental data, giving us support to estimate the gas-phase enthalpies of formation of the remaining isomers whose values have not been determined experimentally.A simple group additivity scheme was successfully applied for prediction of molar enthalpies of formation.The computational study was also extended to the determination of OH bond dissociation enthalpies for all the isomers.

Interactions between substituents in the benzene ring. Experimental and theoretical study of methoxy substituted acetophenones

The mutual interaction of substituents in the aromatic ring is one of the fundamentals of organic chemistry. Acetyl and methoxy substituted benzenes are abundant in value added lignin valorisation products. Using the transpiration method, the absolute vapor pressures of methoxy-acetophenones were measured and used to calculate the standard molar enthalpies of vaporisation. The new thermodynamic results and those available in the literature were evaluated in this work using structure–property correlations. The gas-phase standard molar enthalpies formation of methoxy-acetophenones were estimated using a high-level quantum chemical method G4. The pair-wise interactions of acetyl and methoxy substituents were derived in the frame of a “centerpiece” group-contribution approach. It was shown that in the case of agglomeration of up to three substituents in the benzene ring, no additional interactions are generally required for a reliable prediction of the thermodynamic properties of value-added compounds from lignin utilization processes.

Experimental and Theoretical Investigation on the Thermochemistry of 3-Methyl-2-benzoxazolinone and 6-Nitro-2-benzoxazolinone.

The determination of the reliable thermodynamic properties of 2-benzoxazolinone derivatives is the main goal of this work. Some correlations are established between the energetic properties determined and the structural characteristics of the title compounds, and the reactivity of this class of compounds is also evaluated. Static-bomb combustion calorimetry and high-temperature Calvet microcalorimetry were used to determine, respectively, the standard molar enthalpies of formation in the solid state and the standard molar enthalpies of sublimation, both at T = 298.15 K. Using the results obtained for each compound, the respective gas-phase standard molar enthalpy of formation was derived. High-level quantum chemical calculations were performed to estimate the same property and the results evidence good accordance. Moreover, the gas-phase relative thermodynamic stability of 2-benzoxazolinone derivatives was also evaluated using the respective gas-phase standard molar Gibbs energy of formation. In addition, the relationship between the energetic and structural characteristics of the benzoxazolinones is presented, evidencing the enthalpic increments associated with the presence of a methyl and a nitro groups in the molecule, and this effect is compared with similar ones in other structurally related compounds.

JPCRD: 50 Years of Providing the Scientific Community with Critically Evaluated Thermodynamic Data, Predictive Methods, and Large Thermodynamic Data Compilations

A brief overview is provided on articles published in the Journal of Physical and Chemical Reference Data containing experimental thermodynamic data as well as group contribution methods used to predict thermodynamic quantities of organic compounds. Published papers have contained large compilations of experimental and calculated condensed-phase and gas-phase standard molar enthalpies of formation, isobaric molar heat capacities, molar enthalpies of fusion, molar enthalpies of sublimation, and molar enthalpies of vaporization.

Weaving a web of reliable thermochemistry around lignin building blocks: phenol, benzaldehyde, and anisole

Abstract Substituted benzenes such as phenol, benzaldehyde, and anisole are the simplest fragments from the lignin separation feedstocks. We have collected available primary experimental results on vapour pressures, enthalpies of phase transition, and enthalpies of combustion of phenol, benzaldehyde, and anisole. The resulting data on the gas-phase standard molar enthalpies of formation were validated using the quantum chemical method G4. The consistent sets of evaluated thermodynamic data are essential for calculating the energy balances of lignin conversion in the value-added chemicals and materials. Graphic abstract

An accurate prediction of oxidation potential for a series of phenylthiophene derivatives

The high-level composite G4 method is used to calculate the gas phase standard molar enthalpies of formation (ΔHf,298) for a series of 3-(para-X-phenyl)thiophenes (PTs), in which X is referred to as the -CH3, -OCH3, -H, -F, and -C1 substituents. The accurate oxidation potential (Eox) values are also calculated with respect to the Ag/AgCl reference electrode in acetonitrile. The results show that the theoretical and experimental Eox values are in excellent agreement with each other; these quantities successfully reveal a linear correlation with various electronic characteristics of PTs. A linear dependence behavior on the Hammett constants of the substitutions can be seen for the Eox values. Analysis of the HOMO-LUMO band gap and the UV–visible spectral properties demonstrate the facility of hole transport for the PTs as a potential candidate for conducting polymers.

Energetic and Structural Studies of Two Biomass-Derived Compounds: 6- and 7-hydroxy-1-indanones

The energetic study of 6-hydroxy-1-indanone and 7-hydroxy-1-indanone was performed using experimental techniques and computational calculations. The enthalpies of combustion and sublimation of the two compounds were determined and allowed to derive the corresponding gas-phase standard molar enthalpies of formation. For this purpose, static-bomb combustion calorimetry and drop-method Calvet microcalorimetry were the experimental techniques used. Further, the enthalpy of fusion of each compound was obtained from scanning differential calorimetry measurements. Additionally, the gas-phase standard molar enthalpies of formation of these compounds were calculated through high-level ab initio calculations. The computational study of the molecular structures of the indanones was carried out and two possible conformers were observed for 6-hydroxy-1-indanone. Furthermore, the energetic effects associated with the presence of one hydroxyl group as a substituent on the benzenic ring of 1-indanone were also evaluated. Both experimental and theoretical methods show that 7-hydroxy-1-indanone is thermodynamically more stable than the 6-isomer in the gaseous phase and these results provide evidence for the existence of a strong intramolecular H-bond in 7-hydroxy-1-indanone. Finally, the intramolecular proton transfer in 7-hydroxy-1-indanone has been evaluated and as expected, it is not energetically favorable.

Energetics of tetradentate N2O2 schiff bases containing different alkyldiimine brigdes

This work is part of a comprehensive study of the thermal properties of several molecules of tetradentate Schiff bases, obtained as condensation products of salicylaldehyde with alkyldiamines. Herein, we report an experimental thermochemical study of SALPN (N,N′-bis(salicylaldehydo)propylenediimine) and a computational thermochemical study of SALEN (N,N′-bis(salicylaldehydo)dimethylenediimine), SALPN and SALBUTEN (N,N′-bis(salicylaldehydo)tetramethylenediimine) ligands.The standard (p° =0.1 MPa) molar enthalpy of formation of crystalline SALPN, at T = 298.15 K, was determined using the static-bomb calorimetry technique. Also, the enthalpy of fusion of this ligand has been determined by differential scanning calorimetry. Additionally, using quantum chemical calculations at the CCSD(T) level of theory, we have calculated the gas-phase standard molar enthalpies of formation of three Schiff base ligands, SALEN, SALPN and SALBUTEN. Moreover, a computational study of the molecular structures of the ligands has been carried out.

Ionic liquids alkyl-imidazolium thiocyanates: Comprehensive thermochemical study

Ionic liquids containing imidazolium cation and thiocyanate anion are attracting considerable attention for industrial applications due to low viscosities, low melting points and good conductivity. A comprehensive thermodynamic study of [Cnmim][SCN] series with (n = 2, 4, and 6) was performed in this paper. Vapor pressures were measured by using the quartz-crystal microbalance (QCM). Vaporization enthalpies have been derived by using thermogravimetry and QCM and adjusted to the reference temperature 298.15 K. An absence of possible thermal decomposition during vapor pressure measurements was monitored by the ATR-IR spectroscopy. The liquid phase standard molar enthalpy of formation of [C4mim][SCN] was measured by using combustion calorimetry, combined with the evaluated vaporization enthalpy to get gas-phase standard molar enthalpy of formation. The latter experimental value was in close agreement with theoretical gas-phase molar enthalpy of formation of [C4mim][SCN], calculated by the high-level quantum chemical method G3MP2. These experimental and theoretical results were applied for estimation of aqueous standard molar enthalpies of formation of [Cnmim] cations, as well as for calculation of solubilities of practically relevant solutes in of [Cnmim][SCN] series of ionic liquids.

Calorimetric and computational study of (1H-Indol-n-yl)methanol and 2-(1H-Indol-n-yl)ethanol (n=2, 3)

In the present work, the gas-phase standard molar enthalpy of formation of 2-(1H-indol-3-yl)ethanol was derived, at T = 298.15 K, from the enthalpy of combustion for the crystalline compound, measured by static-bomb calorimetry, and its enthalpy of sublimation obtained from Calvet microcalorimetry measurements. The standard molar enthalpies of formation of this compound and for (1H-indol-2-yl)methanol, (1H-indol-3-yl)methanol and 2-(1H-indol-2-yl)ethanol were calculated using the composite G3 method. The experimental value of the gas-phase enthalpy of formation of 2-(1H-indol-3-yl)ethanol is ‒(48.5 ± 3.3) kJ mol−1, being in excellent agreement with the G3 value, thus giving confidence to the estimates. The results were analysed in terms of the enthalpic methylene increments and compared with other related systems.

Thermodynamic properties of ε-caprolactam and ε-caprothiolactam

This paper is concerned with experimental and computational thermochemical studies of ε-caprolactam and ε-caprothiolactam, molecules whose flexible ring structure provides several conformational forms.The gas-phase standard enthalpy of formation at the reference temperature of 298.15 K of the two title compounds have been determined from the enthalpy of formation in the crystalline phase, derived from bomb combustion calorimetry, and from the enthalpy of sublimation, derived from Calvet microcalorimetry and Knudsen effusion techniques.The equilibrium geometries and the thermodynamic properties of three minimum energy conformers obtained with the composite G3(MP2)//B3LYP approach were used to determine the conformational composition of the two lactam derivatives, by means of Boltzmann’s distribution. The computed gas-phase standard molar enthalpies of formation of ε-caprolactam and ε-caprothiolactam have been determined using hypothetical gas-phase reactions, taking into account the conformational compositions of each one of the species. This parameter together with the corresponding experimental one are compared.

Energetic vs structural study of two biomass degradation derivatives: 2-Cyclopentenone and 3-methyl-2-cyclopentenone

The standard molar enthalpies of formation in the gaseous state, at T = 298.15 K, of the 2-cyclopentenone and 3-methyl-2-cyclopentenone were derived from their standard molar energies of combustion and from their standard molar enthalpies of vaporization, obtained from static-bomb combustion calorimetry measurements and high-temperature Calvet microcalorimetry, respectively. The enthalpies of hydrogenation of the two cyclopentenones were derived from their gas-phase enthalpies of formation and the gas-phase enthalpies of formation of the corresponding cycloalkanones. The gas-phase standard molar enthalpy of formation of the compounds studied were also obtained using high level ab initio calculations and are in very good agreement with the experimental ones. In addition, thermochemical parameters associated to 2-cyclopentenone and 3-methyl-2-cyclopentenone transformations were investigated using the G3(MP2)//B3LYP level of theory. The conversions of both compounds to longer chain alkanes were found to be thermodynamically favourable.

Thermodynamic properties of naphthoxazole and naphthothiazole derivatives: Experimental and computational studies

Abstract The energetic study of 2-methylnaphtho[1,2- d ]oxazole ( MN12O ), 2-methylnaphtho-[2,3- d ]oxazole ( MN23O ) and 2-methylnaphtho[1,2- d ]thiazole ( MN12T ) has been performed experimental and computationally. The enthalpies of combustion and sublimation/vaporization of these compounds were determined, respectively, from static or rotating bomb combustion calorimetry and high temperature Calvet microcalorimetry and/or the Knudsen-effusion studies. These experimental data allow derivation of the corresponding gas-phase standard molar enthalpies of formation of the three compounds. Additionally, we have obtained the gas-phase standard molar enthalpies of formation of these three compounds, as well of the 2-methylnaphtho[2,3- d ]thiazole ( MN23T ), through high level ab initio calculations, at the G3(MP2)//B3LYP and DLPNO-CCSD(T)/cc-pVTZ levels of theory. The computational study of the molecular structures of the compounds has been carried out. Furthermore, a relationship between the energetic and structural characteristics of these molecules was also evaluated.

Energetic characterization of indanone derivatives involved in biomass degradation

The energetic study of 6-methyl-1-indanone, 6-methoxy-1-indanone and 5,6-dimethoxy-1-indanone has been developed using calorimetric techniques and a computational methodology. The enthalpies of combustion and of sublimation of these compounds were determined from, respectively, static-bomb combustion calorimetry and high-temperature Calvet microcalorimetry. From these experimental data, the gas-phase standard molar enthalpies of formation were derived. Also, the temperature and the enthalpy of fusion of each compound were obtained by differential scanning calorimetry. Additionally, the gas-phase standard molar enthalpies of formation of these compounds were obtained from high-level ab initio calculations, at the G3(MP2)//B3LYP level of theory. The computational approach of these three indanone derivatives allowed us to establish their molecular structures, the co-existence of two and four stable conformations for 6-methoxy-1-indanone and 5,6-dimethoxy-1-indanone, respectively. Furthermore, the energetic effects associated with the presence of one methyl group and one or two methoxy groups in the indanone structure were evaluated. These enthalpic increments were compared with the homologous substitutions in the benzene and naphthalene molecules.

Energetic characterization of a bioactive compound: Uridine

Abstract The standard ( p o = 0.1 MPa) molar enthalpy of formation of crystalline uridine, (C 9 H 12 N 2 O 6 ), was determined from its specific energy of combustion, measured by static bomb combustion calorimetry, in oxygen, at T = 298.15 K, as −(1159.8 ± 1.8) kJ mol −1 . Gas-phase standard molar enthalpy of formation of uridine was determined as −(992.8 ± 3.2) kJ mol −1 from quantum-chemical calculations using the G3(MP2) method. The enthalpy of sublimation of uridine at T = 298.15 K, determined as the difference between standard molar enthalpies of formation of uridine in crystalline and gaseous states, was found to be (167.0 ± 3.7) kJ mol −1 .

Experimental and computational thermochemical study of two fluorobenzazoles: 5-fluoro-2-methylbenzoxazole and 5-fluoro-2-methylbenzothiazole

Abstract An energetic study of 5-fluoro-2-methylbenzoxazole (FMBO) and of 5-fluoro-2-methylbenzothiazole (FMBT), in condensed and gaseous states, has been performed using calorimetric techniques and computational calculations. The standard ( p ∘ = 0.1 MPa ) molar enthalpies of formation of FMBO and FMBT, in the liquid phase, at T = 298.15 K, were derived from the corresponding standard molar energies of combustion, measured by rotating-bomb combustion calorimetry. At T = 298.15 K, the standard ( p ∘ = 0.1 MPa ) molar enthalpy of vaporization, for each compound, was determined, by a direct method, using the vacuum drop microcalorimetric technique. For each compound, from this last value and from the enthalpy of formation of the liquid compounds, the corresponding standard ( p ∘ = 0.1 MPa ) enthalpy of formation in the gaseous phase has been calculated. Additionally, the gas-phase standard molar enthalpies of formation of these two compounds were estimated computationally at the G3(MP2)//B3LYP level of theory, as well as their gas-phase basicities and proton affinities.

Thermochemical and conformational study of optical active phenylbenzazole derivatives

The energetic study of 2-phenylbenzoxazole (PBO), 2-phenylbenzothiazole (PBT), 2-(2-hydroxyphenyl)benzoxazole (HBO) and 2-(2-hydroxyphenyl)benzothiazole (HBT) has been developed either using experimental techniques or computational calculations. The enthalpies of combustion and of sublimation of these compounds were determined and the gas-phase standard molar enthalpies of formation were derived. The experimental techniques used were static or rotating bomb combustion calorimetry, high temperature Calvet microcalorimetry and/or the Knudsen-effusion method. Additionally, we have obtained the gas-phase standard molar enthalpies of formation of these compounds, as well of 2-(2-hydroxyphenyl)benzimidazole (HBI), through high level ab initio calculations, at the G3(MP2)//B3LYP level. The computational study of the molecular structures of all these compounds has been carried out and four possible conformers were observed for the molecules of each compound, where the keto tautomers have always higher energy than the enol forms. Furthermore, the energetic effects associated to the presence of the hydroxyl group on the core of the 2-phenylbenzazole rings, in particular the hydrogen bond network, were also evaluated.

Energetic and reactivity properties of 9,10-dihydroacridine and diphenylamine: A comparative overview

The purpose of this research was to determine the energetic and reactivity properties of diphenylamine and 9,10-dihydroacridine using computational methodologies. The equilibrium geometries in the gaseous phase of the studied compounds were analysed in detail and the structural effects on the aforementioned properties were assessed. The values of the gas-phase standard molar enthalpies of formation of diphenylamine (217.7±1.8) kJ·mol−1 and 9,10-dihydroacridine (198.7±4.4) kJ·mol−1 were estimated by hypothetical gas-phase reactions using the G3(MP2)//B3LYP composite method. These data were compared with the ones available in the literature, including the gas-phase enthalpy of formation of 9,10-dihydroacridine derived from the assumption of comparability of the enthalpies of hydrogenation in the liquid and gas phases. Other gas-phase thermodynamic properties, namely the bond dissociation enthalpies (NH and CH) and the gas-phase acidities were also determined.The electrostatic potential surfaces and the frontier molecular orbitals were determined for both compounds, allowing us to infer about its reactivity. Other derived properties include the HOMO-LUMO energy gap and the ionization potential.

Aliphatic nitroalkanes: Evaluation of thermochemical data with complementary experimental and computational methods

Thermochemical properties of aliphatic nitroalkanes available in the literature are scarce and inconsistent. New standard molar enthalpies of vaporization and sublimation of 2-nitropropane, 2-methyl-2-nitropropane, and 2,3-dimethyl-2,3-dinitrobutane were derived from the vapor pressure temperature dependence measured by the transpiration method. Thermodynamic data on linear and branched aliphatic mono- and di-nitroalkanes available in the literature were combined with own experimental results and evaluated with help of empirical and theoretical methods aiming at recommendation of the sets of vaporization and formation enthalpies for aliphatic nitroalkanes as the reliable benchmark properties for further thermochemical calculations. Gas phase standard molar enthalpies of formation of aliphatic nitro-compounds derived by high-level quantum-chemical method G4 were found in a good agreement with the evaluated and recommended experimental data. Group-additivity procedure for calculation of vaporization and formation enthalpies have been developed and tested.