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Highlights: [•] Experimental standard molar enthalpies of formation, sublimation of 2- and 3-coumaranone. [•] Mini-bomb combustion calorimetry, sublimation Calvet microcalorimetry. [•] DFT methods and high level composite ab initio calculations. [•] Theoretical estimate of the enthalpy of formation of isobenzofuranone. [•] Chemical shift (NICS) and the relative stability of the isomers. [ABSTRACT FROM AUTHOR]

Highlights: [•] Experimental standard molar enthalpies of formation, sublimation of 2- and 3-coumaranone. [•] Mini-bomb combustion calorimetry, sublimation Calvet microcalorimetry. [•] DFT methods and high level composite ab initio calculations. [•] Theoretical estimate of the enthalpy of formation of isobenzofuranone. [•] Chemical shift (NICS) and the relative stability of the isomers. [ABSTRACT FROM AUTHOR]

Abstract: The present work reports an experimental study on the energetics of 2,1,3-benzothiadiazole and a computational study on its structure, energetics and aromaticity. In the experimental part the standard (p° =0.1MPa) massic energy of combustion, at T =298.15K, was measured by rotating bomb combustion calorimetry, in oxygen, and allowed the calculation of the respective standard molar enthalpy of formation, in the crystalline phase, at T =298.15K. The standard molar enthalpy of sublimation, at T =298.15K, was measured by high-temperature Calvet microcalorimetry. From the combination of data obtained by both techniques we were able to calculate the respective standard molar enthalpy of formation, in the gas phase, at T =298.15K: (276.6±2.5)kJ·mol−1. This thermochemical parameter was compared with estimates obtained from high level ab initio quantum chemical calculations using the G3(MP2)//B3LYP composite method and various appropriately chosen reactions. The molecular structure of 2,1,3-benzothiadiazole was obtained from DFT calculations with the B3LYP density functional and various basis sets: 6-31G(d), 6-311(d,p), 6-311+G(3df,2p), aug-ccpVTZ and aug-ccpVQZ and its aromaticity and that of some related molecules were evaluated by analysis of nucleus independent chemical shifts (NICS) values. [Copyright &y& Elsevier]

Abstract: The standard (p°=0.1MPa) molar energy of combustion in oxygen, at T =298.15K, of 7-hydroxycoumarin was measured by static bomb calorimetry. The value of the standard molar enthalpy of sublimation was obtained by Calvet microcalorimetry and corrected to T =298.15K. Combining these results, the standard molar enthalpy of formation of the compound, in the gas phase, at T =298.15K, has been calculated, −(337.5±2.3)kJ·mol−1. The values for the temperature of fusion, T fusion, and for the fusion enthalpy, at T = T fusion, are also reported. Additionally, high-level density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional with extended basis sets, the MC3BB and MC3MPW methods and more accurate correlated computational techniques of the MCCM suite have been performed for the compound. The agreement between experiment and theory gives confidence to estimate the enthalpy of formation of the remaining hydroxycoumarins substituted in the benzene ring. [Copyright &y& Elsevier]

Abstract: In this work, we have determined the experimental standard molar enthalpies of formation, in the gas phase, of 2,6-dimethyl-4-pyrone −(261.5±2.6)kJ·mol−1 and 2-ethyl-3-hydroxy-4-pyrone −(420.9±2.8)kJ·mol−1. These values were obtained by combining the standard molar enthalpy of formation in the condensed phase, derived from combustion experiments in oxygen, at T =298.15K, in a static bomb calorimeter, with the standard molar enthalpy of sublimation, at T =298.15K, obtained by Calvet microcalorimetry. Additionally, high-level density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional with extended basis sets have been performed for these two compounds. Good agreement was obtained between the experimental and computational results. Using the same methodology, we calculated the standard molar enthalpy of formation of gaseous 2-methyl-3-hydroxy-4-pyrone. [Copyright &y& Elsevier]

Abstract: The present work reports an experimental and computational study of the energetics of 1,2-benzisothiazol-3(2H)-one and 1,4-benzothiazin-3(2H,4H)-one. The standard (p°=0.1MPa) massic energy of combustion, at T =298.15K, of each compound was measured by rotating bomb combustion calorimetry, in oxygen that allowed the calculation of the respective standard molar enthalpy of formation, in the condensed phase, at T =298.15K. The standard molar enthalpies of sublimation, at T =298.15K, were measured by high-temperature Calvet microcalorimetry. From the combination of data obtained by both techniques we have calculated the standard molar enthalpies of formation, in the gaseous phase, at T =298.15K. In addition, computational calculations were carried using the density functional theory with the B3LYP functional and the 6-31G∗ basis set and some correlations between structure and energetics were obtained for the keto and enol forms of both compounds. Using the G3(MP2)//B3LYP composite method and various appropriate reactions, the standard molar enthalpies of formation of 1,2-benzisothiazol-3(2H)-one and 1,4-benzothiazin-3(2H,4H)-one, at T =298.15K, were computationally derived and compared with the experimental data. The aromaticity of 1,2-benzisothiazol-3(2H)-one, 1,4-benzothiazin-3(2H,4H)-one and that of some related species was evaluated by analysis of nucleus independent chemical shifts (NICS). [Copyright &y& Elsevier]

Abstract: A study on the molecular structure and energetics of 10,11-dihydro-5H-dibenzo[a,d]cycloheptene (dibenzosuberane) was performed combining experimental calorimetric techniques and high level computational calculations. In the experimental work, the solid phase standard ( =0.1MPa) molar enthalpy of formation of 10,11-dihydro-5H-dibenzo[a,d]cycloheptene was derived from its standard massic energy of combustion, at T =298.15K, measured by static bomb combustion calorimetry, in oxygen. The respective standard molar enthalpy of sublimation, at T =298.15K, was measured by Calvet microcalorimetry enabling the calculation of the standard molar enthalpy of formation (161.4±3.7)kJ·mol−1, in the gaseous phase, at T =298.15K. In addition, computational calculations were performed using the density functional theory with the B3LYP hybrid functional and extended basis sets in order to obtain the molecular structure of 10,11-dihydro-5H-dibenzo[a,d]cycloheptene and that of related molecules. Estimates of the standard molar enthalpy of formation, in the gaseous phase, at T =298.15K, for 10,11-dihydro-5H-dibenzo[a,d]cycloheptene were performed using three different methods: G3(MP2)//B3LYP, MC3BB, and MC3MPW and appropriate homodesmic reactions. Computational estimates are in very good agreement with the experimental value. [ABSTRACT FROM AUTHOR]

Abstract: An experimental and computational thermochemical study was performed for oxindole. The standard () molar enthalpy of formation of solid oxindole was derived from the standard molar energy of combustion, in oxygen, at T =298.15K, measured by static bomb combustion calorimetry. The respective standard molar enthalpy of sublimation, at T =298.15K, was measured by Calvet microcalorimetry. The standard molar enthalpy of formation in the gas phase was derived as −(66.8±3.2)kJ·mol−1. Density functional theory calculations with the B3LYP hybrid functional and the 6-31G∗ and 6-311G∗∗ sets have also been performed in order to obtain the most stable conformation of oxindole. A comparison has been made between the structure of oxindole and that of the related two-ring molecules: indoline and 2-indanone and the one-ring molecules: pyrrolidine and 2,3-dihydropyrrole. The G3(MP2)//B3LYP method and appropriate reactions were used to obtain estimates of the standard molar enthalpy of formation of oxindole in the gas phase, at T =298.15K. Computationally obtained estimates of the enthalpy of formation of oxindole are in very good agreement with the experimental gas phase value. The aromaticity of oxindole was evaluated through the analysis of the nucleus independent chemical shifts (NICS) obtained from the B3LYP/6-311G∗∗ wave functions. [Copyright &y& Elsevier]

In this work, we have determined the experimental standard (p° =0.1MPa) molar enthalpies of formation, in gas phase, of flavone and flavanone. These results were obtained by combining the standard molar enthalpies of formation in the condensed phase with the standard molar enthalpies of sublimation. The former values were derived from combustion experiments in oxygen, at T =298.15K, in a static bomb calorimeter. The values of the standard molar enthalpies of sublimation were obtained by Calvet microcalorimetry and corrected to T =298.15K. High-level density functional theory calculations using the B3LYP hybrid exchange–correlation energy functional with extended basis sets and more accurate correlated computational techniques of the MCCM/3 suite have been performed for the compounds. The obtained results, experimental and computational, for flavone and flavanone were compared with those obtained for chromone and chromanone, respectively. [Copyright &y& Elsevier]

Abstract: The standard (p ∘ =0.1MPa) molar enthalpies of formation in the condensed state of chromanone, dihydrocoumarin, and 3-isochromanone were derived from the standard molar energies of combustion in oxygen at T =298.15K, measured by combustion calorimetry. Calvet microcalorimetry was used to derive the standard molar enthalpies of sublimation and vaporization. From these values the standard molar enthalpies in the gaseous phase, at T =298.15K, were derived. Additionally estimates were performed of the enthalpies of formation of all the studied compounds in gas-phase, using DFT and other more accurate correlated calculations, together with appropriate isodesmic or homodesmic reactions. There is a reasonable agreement between computational and experimental results. [Copyright &y& Elsevier]

Abstract: The standard (p ∘ =0.1MPa) molar energies of combustion in oxygen, at T =298.15K, of 5-, 6- and 7-methoxy-α-tetralone were measured by static bomb calorimetry. The values of the standard molar enthalpies of sublimation were obtained by Calvet microcalorimetry and corrected to T =298.15K. Combining these results, the standard molar enthalpies of formation of the compounds, in the gas phase, at T =298.15K, have been calculated, 5-methoxy-α-tetralone -(244.8±1.9)kJ·mol−1, 6-methoxy-α-tetralone −(243.0±2.8)kJ·mol−1 and 7-methoxy-α-tetralone −(242.3±2.6)kJ·mol−1. Additionally, high-level density functional theory calculations using the B3LYP hybrid exchange–correlation energy functional with extended basis sets and more accurate correlated computational techniques of the MCCM/3 suite have been performed for the compounds. The agreement between experiment and theory gives confidence to estimate the enthalpy of formation of 8-methoxy-α-tetralone. Similar calculations were done for the 5-, 6-, 7- and 8-methoxy-β-tetralone, for which experimental work was not done. [Copyright &y& Elsevier]

Abstract: The standard molar energies of combustion, at T =298.15K, of crystalline 1,4-benzodioxan-2-carboxylic acid and 1,4-benzodioxan-2-hydroxymethyl were measured by static bomb calorimetry in an oxygen atmosphere. The standard molar enthalpies of sublimation, at T =298.15K, were obtained by Calvet microcalorimetry. These values were used to derive the standard molar enthalpies of formation of the compounds in the gas phase at T =298.15K: 1,4-benzodioxan-2-carboxylic acid −(547.7±3.0)kJ·mol−1 and 1,4-benzodioxan-2-hydroxymethyl −(374.2±2.3)kJ·mol−1. In addition, density functional theory calculations using the B3LYP hybrid exchange–correlation energy functional with extended basis sets, 6-311G∗∗ and cc-pVTZ, have been performed for the compounds studied. We have also tested two more accurate computational procedures involving multiple levels of electron structure theory in order to get reliable estimates of the thermochemical parameters of the compounds studied. The agreement between experiment and theory gives confidence to estimate the enthalpies of formation of other 2-R derivatives of 1,4-benzodioxan (R=–CH2COOH, –OH, –COCH3, –CHO, –CH3, –CN, and –NO2). [Copyright &y& Elsevier]

Abstract: The standard (p ∘ =0.1MPa) molar enthalpies of combustion and sublimation of 3,4,5-trimethoxyphenol were measured, respectively, by static bomb combustion calorimetry in oxygen atmosphere and by Calvet microcalorimetry. From these measurements, the standard molar enthalpy of formation in both the crystalline and gaseous phase, at T =298.15K, were derived: −(643.4±1.9)kJ·mol−1 and −(518.1±3.6)kJ·mol−1, respectively. Density functional theory calculations for this compound and respective phenoxyl radical and phenoxide anion were also performed using the B3LYP functional and extended basis sets, which allowed the theoretical estimation of the gaseous phase standard molar enthalpy of formation through the use of isodesmic reactions and the calculation of the homolytic and heterolytic O–H bond dissociation energies. There is good agreement between the calculated and experimental enthalpy of formation. Substituent effects on the homolytic and heterolytic O–H bond dissociation energies have been analysed. [Copyright &y& Elsevier]

The standard (p° = 0.1 MPa) molar energies of combustion in oxygen, at T = 298.15 K, of 1-naphthalenemethanol and 2-naphthalenemethanol were measured by static bomb calorimetry. The values of the standard molar enthalpies of sublimation, at T = 298.15 K, were obtained by Calvet microcalorimetry. Combining these results the standard molar enthalpies of formation of the compounds, in the gas phase, at T = 298.15 K, have been calculated. [image omitted] (kJ·mol-1) [image omitted] (kJ·mol-1) [image omitted] (kJ·mol-1) 1-Naphthalenemethanol 132.5 ± 2.9 102.3 ± 1.9 30.2 ± 3.5 2-Naphthalenemethanol 134.9 ± 3.3 106.0 ± 2.1 28.9 ± 3.9 Density functional theory with the B3LYP functional and two different basis sets, 6-31G(d) and 6-311G(d, p), were used to optimize the geometries of the two substituted naphthalenes. Additionally, ab initio second order Møller-Plesset calculations were also used at the MP2(FULL)/6-31G(d), MP2/6-31 + G(d), and MP2(FULL)/6-31 + G(d) levels. The calculation of the energies of appropriate isodesmic reactions allowed the estimation of the standard molar enthalpies of formation in the gas phase for the compounds. The experimental measurements and both sets of quantum chemical calculations were in good agreement for both isomers. [ABSTRACT FROM AUTHOR]

The standard molar enthalpy of formation in the gas phase of 2H-1,4-benzoxazin-3(4H)-one was derived from the standard energy of combustion determined by static bomb combustion calorimetry in oxygen atmosphere and from the standard sublimation enthalpy determined by Calvet microcalorimetry. In addition, we report the results of a systematic theoretical study of the keto and enol tautomers in benzoxazinones and diones using density functional theory. The keto tautomers are computed to be more stable than the enols. Tautomerization energies are reported. [ABSTRACT FROM AUTHOR]

The standard molar enthalpies of combustion, sublimation, and formation of three nitrogen-containing heterocycles, namely, 2-benzimidazolinone, 2-benzoxazolinone and 3-indazolinone were determined calorimetrically. The standard ( p °?=?0.1?MPa) molar enthalpies of formation in the gas phase were derived from the standard molar enthalpies of combustion, in oxygen, at T ?=?298.15?K, measured by static bomb combustion calorimetry and from the standard molar enthalpies of sublimation at T ?=?298.15?K, measured by Calvet microcalorimetry. Møller–Plesset calculations at the MP2 level and density functional calculations with the B3LYP functional and extended basis sets were also performed to determine the energetically preferred tautomeric form of the molecules. The results were qualitatively independent of the calculational level, where in general the DFT calculations were in better agreement with experiment than those from MP2. The gas and solid phase enthalpic differences between imines and amides, wherein –CH=N- is contrasted with –CONH-, have been studied and roughly constant values have been found. [ABSTRACT FROM AUTHOR]

The standard molar enthalpy of formation for liquid sulpholane was derived from the standard molar enthalpy of combustion, in oxygen at T = 298.15 K, measured by rotating bomb combustion calorimetry. The standard molar enthalpy of vaporization, at T = 298.15 K, was measured by Calvet microcalorimetry. The results are: ; ; and . Additionally, high-level density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional have been performed for sulpholane in order to obtain its geometry, enthalpy of formation in the gaseous phase and strain energy. [ABSTRACT FROM AUTHOR]

The standard ( po = 0.1 MPa) molar enthalpies of formation for 2-, 3-, and 4- trans -methoxycinnamic acids in the gaseous phase were derived from the standard molar enthalpies of combustion in oxygen of the crystalline compounds determined by static bomb combustion calorimetry atT = 298.15 K and from the literature values for the respective enthalpies of sublimation. [Copyright &y& Elsevier]

Abstract: The standard (p =0.1MPa) molar enthalpy of formation of 6,7-dihydro-4(5H)-benzofuranone was measured, at T =298.15K, by static bomb calorimetry and the standard molar enthalpy of vaporization, at T =298.15K, was obtained using Calvet microcalorimetry. These values were combined together to derive the standard molar enthalpy of formation of the title compound in gaseous phase, at T =298.15K, −(226.0±2.8)kJ·mol−1. Display Omitted Additionally, density functional theoretical calculations using the B3LYP hybrid exchange-correlation energy functional with extended basis sets and also other higher-level ab initio quantum calculations have been performed. [Copyright &y& Elsevier]

Abstract: This paper reports a combined thermochemical experimental and computational study of the two isomers 3- and 4-hydroxycoumarin. The standard () molar enthalpies of formation in the condensed state of the compounds were derived from the standard molar energies of combustion in oxygen at T =298.15K, measured by combustion calorimetry. Calvet microcalorimetry was used to derive the standard molar enthalpies of sublimation. By combining these values, the standard molar enthalpies of formation in the gaseous phase, at T =298.15K, were derived −(367.7±1.9)kJ·mol−1 for 3-hydroxycoumarin and −(351.4±2.4) kJ·mol−1 for 4-hydroxycoumarin. The temperatures of fusion, T fus, and fusion enthalpies, at T = T fus, are also reported. Additionally, high-level density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional with extended basis sets, as well as more sophisticated calculations using Doubly Hybrid Density Functional Theory (DHDFT) and more accurate correlated computational techniques of the MCCM suite have been performed for both compounds. The aromaticity of the hydroxycoumarins has been studied using Nucleus Independent Chemical Shifts (NICS) techniques and compared to that of non-substituted coumarin. [ABSTRACT FROM AUTHOR]

Abstract: The energetics of 1-benzosuberone was studied by a combination of calorimetric techniques and computational calculations. The standard (p°=0.1MPa) molar enthalpy of formation of 1-benzosuberone, in the liquid phase, was derived from the massic energy of combustion, in oxygen, at T =298.15K, measured by static bomb combustion calorimetry. The standard molar enthalpy of vaporization, at T =298.15K, was measured by Calvet microcalorimetry. From these two parameters the standard (p°=0.1MPa) molar enthalpy of formation, in the gaseous phase, at T =298.15K, was derived: −(96.1±3.4)kJ·mol−1. The G3(MP2)//B3LYP composite method and appropriate reactions were used to computationally calculate the standard molar enthalpy of formation of 1-benzosuberone, in the gaseous phase, at T =298.15K. The computational results are in very good agreement with the experimental value. [Copyright &y& Elsevier]

Abstract: The structure and energetics of the methoxy-derivatives of coumarin with the substituent either on the benzenic ring (5-, 6-, 7- and 8-methoxy coumarin) or on the pyrone ring (3- and 4-methoxycoumarin) is addressed on the basis of some well documented computational methods. Estimates of the enthalpies of formation are obtained using appropriate homodesmotic reactions and also atomization reactions. The condensed phase standard (p 0 =0.1MPa) molar enthalpy of formation for 7-methoxycoumarin was derived from the standard molar enthalpy of combustion, in oxygen, at T =298.15K, measured by static bomb combustion calorimetry. The standard molar enthalpy of sublimation, at T =298.15K, was measured by Calvet microcalorimetry. Combining these values, the enthalpy of formation in gas-phase, at T =298.15K, was derived: −(321.6±2.8) kJmol−1. The temperature of fusion, T fusion, and fusion enthalpies, at T = T fusion, are also reported. Good agreement between experimental and computational data is achieved. The aromaticity of these systems has been assessed through the evaluation and analysis of the Nucleus Independent Chemical Shifts (NICS) and their most significant components. NICS scan analyses have also been conducted to help clarifying the aromatic nature of the pyrone rings of these systems. [Copyright &y& Elsevier]

Abstract: The standard (p ∘ =0.1MPa) molar energy of combustion, at T =298.15K, of crystalline 2,3-dicyanopyrazine was measured by static bomb calorimetry, in oxygen atmosphere. The standard molar enthalpy of sublimation, at T =298.15K, was obtained by Calvet Microcalorimetry, allowing the calculation of the standard molar enthalpy of formation of the compound, in the gas phase, at T =298.15K: (g)=(518.7±3.4)kJ·mol−1. In addition, the geometries of all cyanopyrazines were obtained using density functional theory with the B3LYP functional and two basis sets: 6-31G* and 6-311G**. These calculations were then used for a better understanding of the relation between structure and energetics of the cyanopyrazine systems. These calculations also reproduce measured standard molar enthalpies of formation with some accuracy and do provide estimates of this thermochemical parameter for those compounds that could not be studied experimentally, namely the tri- and tetracyanopyrazines: the strong electron withdrawing cyano group on the pyrazine ring makes cyanopyrazines highly destabilized compounds. [Copyright &y& Elsevier]

Radical anions of O-, m-, and p-benzoquinone were produced in a Fourier transform mass spectrometer by low energy electron attachment or collision-induced dissociation and were differentiated. Classical derivatization experiments also were carried out to authenticate the ortho and meta anions. Gas- phase techniques were used to measure the proton affinities of all three radical anions and the electron affinities of o- and m-benzoquinone. By combining these results in thermodynamic cycles, we derived heats of hydrogenation of o-, m-, and p-benzoquinone (AhydHo(1O, 1m, and 1p) = 42.8 ± 4.1, 74.8 ± 4.1, and 38.5 ± 3.0 kcal mol-1, respectively) and their heats of formation (Ad-P(1o, 1 m, and Ip) = -23.1 ± 4.1, 6.8 ± 4.1, and -27.7 ± 3.0 kcal mol-1, respectively). Good accord with the literature value for the para derivative was obtained. Combustion calorimetry and heats of sublimation also were measured for benzil and 3,5- di-tert-butyl-o-benzoquinone. The former heat of formation agreed with previous determinations, while the latter result (AfI-f(g) = -73.09 ± 0.87 kcal mol-1) was transformed to A1H°(lo) = -18.9 ± 2.2 kcal mol-1 by removing the effect of the tert-butyl groups via isodesmic reactions. This led to a final value of AH°(10) = -21.0 ± 3.1 kcal mol-1. Additivity was found to work well for m-benzoquinone, but BDE1 and BDE2 for 1,2- and I ,4-dihydroxybenzene differed by a remarkably small 14.1 ± 4.2 and 23.5 ± 3.7 kcal mol1, respectively, indicating that o- and p-benzoquinone should be excellent radical traps. [ABSTRACT FROM AUTHOR]