M. Agostinha R. Matos

Enthalpies of combustion, vapour pressures, and enthalpies of sublimation of 8-hydroxyquinoline, 5-nitro-8-hydroxyquinoline, and 2-methyl-8-hydroxyquinoline

Abstract The standard ( p o = 0.1 MPa) molar enthalpies of combustion, in oxygen, at 298.15 K, were measured by static bomb calorimetry for three 8-hydroxyquinolines; the vapour pressures of the crystals were measured as functions of temperature by the Knudsen-effusion technique, and the standard molar enthalpies of sublimation, at 298.15 K, were derived by the Clausius-Clapeyron equation. Direct measurements of the standard molar enthalpies of sublimation using micro-calorimetry confirmed the values from the Knudsen technique. −Δ c H m o (cr)/(kJ·mol t 1 ) Δ cr g H m o /(kJ·mol −1 ) Knudsen Calvet 8-Hydroxyquinoline 4459.0±0.9 89.5±0.9 89.0±1.4 5-Nitro-8-hydroxyquinoline 4283.4±1.1 114.1±2.2 111.2±3.0 2-Methyl-8-hydroxyquinoline 5091.5±1.6 90.4±0.7 87.2±1.9

Enthalpies of combustion, vapour pressures, and enthalpies of sublimation of 2-hydroxyquinoline, 4-methyl-2-hydroxyquinoline, 4-hydroxyquinoline, and 2-methyl-4-hydroxyquinoline

Abstract The standard (po = 0.1 MPa) molar enthalpies of formation were derived from the standard molar enthalpies of combustion, in oxygen, at 298.15 K, measured by static bomb calorimetry for 2-hydroxyquinoline (2HOQ), 4-methyl-2-hydroxyquinoline (4Me-2HOQ), 4-hydroxyquinoline (4HOQ), and 2-methyl-4-hydroxyquinoline (2Me-4HOQ); the vapour pressures of the crystals were measured as functions of temperature by the Knudsen-effusion technique, and the standard molar enthalpies of sublimation, at 298.15 K, were derived by the Clausius-Clapeyron equation. −Δ f H m o (cr)/(kJ · mol −1 ) Δ cr 8 H m o /(kJ · mol −1 ) 2HOQ 144.9 ± 2.3 119.4 ± 0.6 4Me-2OHQ 189.1 ± 2.8 128.1 ± 1.6 4HOQ 114.3 ± 2.0 135.1 ± 1.1 2Me-4HOQ 162.3 ± 2.7 139.0 ± 1.0

Energetics of Coumarin and Chromone

Condensed phase standard (p degrees = 0.1 MPa) molar enthalpies of formation for coumarin and chromone were derived from the standard molar enthalpies of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The standard molar enthalpies of sublimation, at T = 298.15 K, were measured by Calvet microcalorimetry. Combining these values, the following enthalpies of formation in the gas phase, at T = 298.15 K, were then derived: coumarin, -(163.4 +/- 3.3) kJ x mol(-1), and chromone, -(126.1 +/- 2.5) kJ x mol(-1). The temperatures of fusion, T(fusion), and fusion enthalpies, at T = T(fusion), were also reported. Additionally, theoretical calculations were done using different methods: DFT/B3LYP, MCCM (MC-UT/3 and MC-QCISD/3), and also the more accurate G3MP2 method. Good agreement between experimental and theoretical data was achieved. Some correlations between structure and energy were also made, and the aromaticity of the compounds was evaluated by the nucleus independent chemical shifts (NICS).

Saccharin: a combined experimental and computational thermochemical investigation of a sweetener and sulfonamide

The standard molar enthalpies of combustion, sublimation, and formation in the crystalline and gaseous phase at a temperature of 298.15 K have been experimentally determined for saccharin and for benzenesulfonamide. These compounds were also studied theoretically using density functional theory, the B3LYP functional and extended basis sets.

Are isatin and isatoic anhydride antiaromatic and aromatic respectively? A combined experimental and theoretical investigation

This paper reports the results of our thermochemical/calorimetric determination of the enthalpies of combustion, phase change, and formation of isatin, isatoic anhydride, and N-methylisatin. The density functional calculations accompanied by vibrational and thermal corrections were also performed for these compounds and N-methylisatoic anhydride. Through a combination of theoretical calculations and associated isodesmic reactions, we have deduced that isatin has some antiaromatic character and isatoic anhydride enjoys some aromatic stabilization.

Standard Enthalpies of Formation of 2,6-Di-tert-butyl4-methylphenol and 3,5-Di-tert-butylphenol and Their Phenoxy Radicals

The standard (po = 0.1 MPa) enthalpies of formation of 2,6-di-tert-butyl-4-methylphenol and 3,5-di-tert-butylphenol in the gaseous phase, −315.5 ± 4.4 kJ mol−1 and −312.7 ± 4.6 kJ mol−1, respectively, were derived from the standard enthalpies of combustion, in oxygen, at 298.15 K, measured by static bomb combustion calorimetry, and from the standard enthalpies of sublimation, at 298.15 K, measured by Calvet microcalorimetry. The O—H bond dissociation enthalpies in those compounds were determined in benzene by photoacoustic calorimetry, leading to the standard enthalpies of formation of the gaseous phenoxy radicals: −189 ± 8 kJ mol−1 and −154 ± 6 kJ mol−1, respectively. These results were used to calculate enthalpies of substituent redistribution reactions, which are proposed as a method to estimate new data for substituted phenols.

THERMOCHEMICAL AND THEORETICAL STUDIES OF 4-METHYLBIPHENYL, 4,4'-DIMETHYLBIPHENYL, 4,4'-DIMETHYL-2,2'-BIPYRIDINE

The standard (p°=0.1 MPa) molar enthalpies of formation for 4-methylbiphenyl, 4,4′-dimethylbiphenyl and 4,4′-dimethyl-2,2′-bipyridine were derived from the standard molar enthalpies of combustion, in oxygen, at T=298.15 K, measured by static-bomb combustion calorimetry. The standard molar enthalpies of sublimation, at T=298.15 K, were measured by Calvet microcalorimetry. Theoretical calculations at the ab initio restricted Hartree–Fock (RHF) level with second-order Moller–Plesset (MP2) perturbation theory correlation corrections and density functional theory (DFT) have been carried out for all these molecules in order to access their stabilitites relative to the non-substituted ones. The theoretical results are in general good agreement with the experimental results.

Study of energetics and structure of 1,2,3-benzotriazin-4(3H)-one and its 1H and enol tautomers.

This paper reports an experimental and computational study on the energetics of 1,2,3-benzotriazin-4(3H)-one. The standard (p° = 0.1 MPa) molar enthalpy of formation of solid 1,2,3-benzotriazin-4(3H)-one, at T = 298.15 K, was derived from its standard massic energy of combustion measured by static bomb combustion calorimetry in oxygen. The Calvet high-temperature vacuum sublimation technique was used to measure the respective standard molar enthalpy of sublimation at T = 298.15 K. From these two experimentally determined thermodynamic parameters, we have calculated the standard molar enthalpy of formation of 1,2,3-benzotriazin-4(3H)-one in the gas phase at T = 298.15 K, (200.9 ± 3.8) kJ·mol(-1). Interrelations between structure and energy for 1,2,3-benzotriazin-4(3H)-one, the tautomer 1,2,3-benzotriazin-4(1H)-one, and the enol tautomer 1,2,3-benzotriazin-4-ol were discussed based on density functional theory (DFT) calculations with the B3LYP hybrid functional and the 6-311++G(d,p) basis set. The gas-phase enthalpy of formation of 1,2,3-benzotriazin-4(3H)-one was estimated from quantum chemical calculations using the G3(MP2)//B3LYP composite method. Nucleus-independent chemical shifts (NICS) were also calculated with the purpose of analyzing the aromaticity of the benzenic and heterocyclic rings of the title molecule and others related tautomerically to it.

Thermochemical and theoretical studies of some benzodiazines

The standard molar enthalpies of formation of quinoxaline, quinazoline and phthalazine at 298.15 K in the gaseous state have been determined from the standard molar enthalpies of combustion of the crystalline solids and the respective enthalpies of sublimation: quinoxaline, 240.3 ± 3.3 kJ mol–1; quinazoline, 243.1 ± 2.7 kJ mol–1; phthalazine, 329.9 ± 3.3 kJ mol–1. Ab initio full geometry optimizations at the 3-21G and 6-31G* levels were also performed for these molecules. MP2/RHF/3-21G//3-21G energies were calculated for all isomers, and used to estimate their isodesmic resonance energies.

Thermochemical study of the ethylpyridine and ethylpyrazine isomers

The standard (p(o) = 0.1 MPa) molar energies of combustion in oxygen, at T = 298.15 K, of four liquids: 2-ethylpyridine, 4-ethylpyridine, ethylpyrazine and 2,3-diethylpyrazine were measured by static bomb calorimetry in an oxygen atmosphere. The values of the standard molar enthalpies of vaporization, at T = 298.15 K, were obtained by Calvet microcalorimetry, allowing the calculation of the standard molar enthalpies of formation of the compounds, in the gas phase, at T= 298.15 K: 2-ethylpyridine (79.4 +/- 2.6) kJ mol(-1); 4-ethylpyridine (81.0 +/- 3.4) kJ mol(-1); ethylpyrazine (146.9 +/- 2.8) kJ mol(-1); and 2,3-diethylpyrazine (80.2 +/- 2.9) kJ mol(-1). The most stable geometries of all ethylpyridine and ethylpyrazine isomers were obtained using the density functional theory with the B3LYP functional and two basis sets: 6-31G* and 6-311G**. These calculations were then used to obtain estimates of the enthalpies of formation of all isomers, including those not experimentally studied, through the use of isodesmic reactions. A discussion of the relationship between structure and energetics of the isomers is also presented.