M. A. R. Matos

Experimental and computational thermochemistry of three nitrogen-containing heterocycles: 2-benzimidazolinone, 2-benzoxazolinone and 3-indazolinone

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.

Thermochemical and theoretical study of some methyldiazines

The standard (p0 = 0.1 MPa) molar enthalpies of formation for the liquid 2,3-dimethylpyrazine and trimethylpyrazine and the crystalline 2,3-dimethylquinoxaline and tetramethylpyrazine were derived from the standard molar enthalpies of combustion, in oxygen, atT=298.15 K, measured by static-bomb combustion calorimetry. The standard molar enthalpies of vaporization or of sublimation for the same compounds were determined by Calvet microcalorimetry. Ab initio full geometry optimization at the 3-21G and 6-31G* levels were also performed for all the methylpyrazine isomers. MP2/RHF/3-21G//3-21G and DFT energies were also calculated for all the methylpyrazine isomers, thus allowing us to estimate their isodesmic resonance energies.

Recent work on the thermochemistry of some nitrogen heterocycles

Values available in the literature for standard molar enthalpies of formation, both in the condensed and in the gaseous phases, at temperature 298.15 K, for quinolines, methylquinolines, hydroxyquinolines, methylhydroxyquinolines, amino- quinolines, cyanoquinolines, halohydroxyquinolines and nitroquinolines are reviewed, and the results are interpreted in terms of contribuitions of the different groups and of molecular structure.

Benzanilide: on the crossroads of calorimetry, computations and concepts

The standard (p° = 0.1 MPa) molar enthalpy of formation for solid benzanilide was derived from the standard molar enthalpy of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry, and the standard molar enthalpy of sublimation, at T = 298.15 K, measured by Calvet microcalorimetry. From these experiments the standard molar enthalpy of formation of benzanilide in the gaseous phase at T = 298.15 K was calculated. In addition density functional theory calculations with the B3LYP functional and a variety of basis sets have been performed for benzanilide and some auxiliary molecules.

Energetics of naphthalene derivatives, IV+: a calorimetric and calculational thermochemical study of the isomeric naphthalenemethanols

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. (kJ·mol−1) (kJ·mol−1) (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. +Paper III: Roux, M.V., Temprado, M., Notario, R., Verevkin, S.P., Emel’yanenko, V.N., DeMasters, D.E., Liebman, J.F. Mol. Phys., 102, 1909 (2004).