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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. 相似文献
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A calorimetric method was applied at 25 °C to measure the enthalpies of dissolution of cyclohexane, heptane, and decane in
the methanol-n-butanol mixed solvent and hexadecane in mixtures of methanol withn-, iso-, andtert-butyl alcohols. The standard enthalpies of dissolution of alkanes were determined. It was shown that the equation proposed
in the literature for calculation of the enthalpies of dissolution of alkanes in mixtures with nonspecific intermolecular
solvent-solvent interactions describes satisfactorily the enthalpies of dissolution of alkanes in mixtures of methanol withn- andiso-butyl alcohols. It was suggested that there is no preferential solvation of alkanes by one of the mixed solvent components
in the MeOH−BunOH and MeOH−BuiOH mixtures; in the MeOH−ButOH system, the composition of alkane solvation shell differs slightly from the solvent composition in the bulk.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 271–274, February, 1999. 相似文献
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M. Agostinha R. Matos Clara C.S. Sousa Victor M.F. Morais 《The Journal of chemical thermodynamics》2009,41(1):69-73
The standard (p° = 0.1 MPa) molar energies of combustion in oxygen, at T = 298.15 K, 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 = 298.15 K. Combining these results, the standard molar enthalpies of formation of the compounds, in the gas phase, at T = 298.15 K, 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. 相似文献
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Maria D. M. C. Ribeiro da Silva Joana I. T. A. Cabral Chelsea Givens Stephanie Keown W. E. Acree Jr. 《Journal of Thermal Analysis and Calorimetry》2008,92(1):73-78
The standard (p
0=0.1 MPa) molar enthalpies of formation, in the gaseous phase, at T-298.15 K, for 2,5-dimethylpyrazine (2,5-DMePz) and for the two dimethylpyrazine-N,N′-dioxide derivatives, 2,3-dimethylpyrazine-1,4-dioxide (2,3-DMePzDO) and 2,5-dimethylpyrazine-1,4-dioxide (2,5-DMePzDO), were
derived from the measurements of standard massic energies of combustion, using a static bomb calorimeter, and from the standard
molar enthalpies of vaporization or sublimation, measured by Calvet microcalorimetry.
The mean values for the molar dissociation enthalpy of the nitrogen-oxygen bonds, 〈DH
m0〉(N-O), were derived for both N,N′-dioxide compounds. These values are discussed in terms of the molecular structure of the two N,N′-dioxide derivatives and compared with 〈DH
m0〉(N-O) values previously obtained for other N-oxide derivatives. 相似文献
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V. V. Avdonin E. I. Kirpichev Va. I. Rubtsov L. B. Romanova M. E. Ivanova L. T. Eremenko 《Russian Chemical Bulletin》1996,45(10):2342-2344
The thermochemical study of cubane-1,4-dicarboxylic acid (1), diethyl cubane-1,4-dicarboxylate (2), diisopropyl cubane-1,4-dicarboxylate (3), and bis(2-fluoro-2,2-dinitro)ethyl cubane-1,4-dicarboxylate (4) was performed. The standard enthalpies of combustion (c
H°) and formation (f
H°) of these compounds were estimated using the method of combustion in a calorimetric bomb in an oxygen atmosphere. Using the additive group method, calculated values for f
H° of these substances which agreed satisfactorily with the experimental ones were obtained. The strain energies (E
s) of the cubic structure of derivatives1–4 were calculated. It was concluded thatE
s did not change on substitution of hydrogen atoms in cubane for various functional groups and was equal toE
s of the structure of cubane itself. The reliability of the single published value of f
H° in the cubane crystal state, 541.8 kJ mol–1 (129.5 kcal mol–1), was confirmed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2471–2473, October, 1996. 相似文献
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M. A. V. Ribeiro da Silva V. M. F. Morais M. A. R. Matos C. M. A. Rio C. M. G. S. Piedade 《Structural chemistry》1996,7(5-6):329-336
The standard (p
0 = 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. 相似文献
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Manuel A.V. Ribeiro da Silva Ana I.M.C. Lobo Ferreira Ana Rita G. Moreno 《The Journal of chemical thermodynamics》2009,41(1):109-114
The standard (p° = 0.1 MPa) molar enthalpies of formation of 2-, 3-, and 4-chloronitrobenzene isomers, in the crystalline state, at T = 298.15 K, were derived from the standard (p° = 0.1 MPa) massic energies of combustion, in oxygen, at T = 298.15 K, measured by rotating bomb combustion calorimetry. The standard molar enthalpies of sublimation of the isomers, at T = 298.15 K, were obtained by high temperature Calvet microcalorimetry.
Empty Cell | /(kJ · mol?1) | /(kJ · mol?1) | /(kJ · mol?1) |
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2-Chloronitrobenzene | 2939.5 ± 0.7 | 18.7 ± 1.0 | 80.9 ± 1.5 |
3-Chloronitrobenzene | 2915.8 ± 0.8 | 42.4 ± 1.2 | 82.5 ± 1.5 |
4-Chloronitrobenzene | 2921.7 ± 1.4 | 36.5 ± 1.6 | 76.2 ± 2.1 |