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- Thermochemical and theoretical study of bipyridinesPublication . Rio, Carolina; Ribeiro da Silva, M. A. V.; Morais, V. M. F.; Matos, M. A. R.The following standard molar enthalpies of formation in the gaseous state at 298.15 K were determined from the enthalpies of combustion of the crystalline solids and the respective enthalpies of sublimation: 2,2’-bipyridine, 267.9 f 3.0 kJ mol-’; 2,4’-bipyridine, 284.2 f 2.7 kJ mol-’; 4,4‘- bipyridine, 293.1 f 3.6 kJ mol-’. Ab initio geometry optimizations of these molecules at the 3-21G level suggest that those with at least one ortho nitrogen atom assume near planar conformations preferentially, while the others have nonplanar most stable forms.
- Thermochemical and theoretical study of some methyldiazinesPublication . Rio, Carolina; Ribeiro da Silva, M. A. V.; Morais, V. M. F.; Matos, M. A. R.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.
- Thermochemical and Theoretical studies of 4-methylbiphenyl, 4,4'-dimethylbiphenyl, 4,4'-dimethyl-2,2'-bipyridinePublication . Rio, CarolinaThe 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 Møller–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.
- Standard molar enthalpy of formation of 2,4,6-trimethylpyridinePublication . Silva, Manuel Ribeiro da; Matos, M. A. R.; Rio, CarolinaThe standard (p°=0.1 MPa) molar enthalpy of formation for liquid 2,4,6-trimethylpyridine was derived from the standard molar enthalpy of combustion, measured by static bomb combustion calorimetry in oxygen, at the temperatureT=298.15 K: ΔfHm=−(31.0±2.3) kJ·mol−1.