The Heats of Combustion and Formation of the Three Diazines and their Resonance Energies.

Tjebbes, Jan; Mollberg, René; Lindberg, Bengt; McKay, James; Theander, Olof; Flood, Hugh D.

doi:10.3891/acta.chem.scand.16-0916

Cited by 91 publications

(39 citation statements)

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“…This suggests that the vapor pressures obtained for pyrimidine as a function of temperature are reasonable, which in turn confirms the magnitude of the vaporization enthalpy measured. This result raises a red flag concerning the vaporization enthalpy of this material reported previously in the literature [4]. Unlike pyrimidine, the BT measured for pyridizine and 3-methylpyridizine are more than 40 K lower than literature values.…”

Section: Resultscontrasting

confidence: 55%

“…This suggests that pyridines and pyrazines are not suitable standards to use for aromatic 1,2-diazines and that the vaporization enthalpies reported in Table 7 for these materials are not to be trusted. In addition to the vaporization enthalpy of pyrimidine and the sublimation enthalpy of pyrazine, Tjebbes [4] also reported the enthalpies of combustion and formation of these diazines. The study of Tjebbes together with the results of this work is summarized in Table 10.…”

Section: Resultsmentioning

confidence: 96%

“…The vaporization enthalpy and vapor pressure measurements obtained for pyridazine and its derivatives by correlation-gas chromatography could not be validated. This study also brings into question the accuracy a previous calorimetric measurement of the vaporization enthalpy of pyrimidine [4]. To the best of our knowledge, this is the only experimental value reported for pyrimidine.…”

Section: Introductionmentioning

confidence: 78%

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An examination of the vaporization enthalpies and vapor pressures of pyrazine, pyrimidine, pyridazine, and 1,3,5-triazine

Lipkind

Chickos

2008

Struct Chem

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The vaporization enthalpies and liquid vapor pressures from T = 298.15 K to T = 400 K of 1,3,5-triazine, pyrazine, pyrimidine, and pyridazine using pyridines and pyrazines as standards have been measured by correlation-gas chromatography. The vaporization enthalpies of 1,3,5-triazine (38.8 ± 1.9 kJ mol -1 ) and pyrazine (40.5 ± 1.7 kJ mol -1 ) obtained by these correlations are in good agreement with current literature values. The value obtained for pyrimidine (41.0 ± 1.9 kJ mol -1 ) can be compared with a literature value of 50.0 kJ mol -1 . Combined with the condensed phase enthalpy of formation in the literature, this results in a gas-phase enthalpy of formation, D f H m (g, 298.15 K), of 187.6 ± 2.2 kJ mol -1 for pyrimidine, compared to a value of 195.1 ± 2.1 calculated for pyrazine. Vapor pressures also obtained by correlation are used to predict boiling temperatures (BT). Good agreement with experimental BT (±4.2 K) including results for pyrimidine is observed for most compounds with the exception of the pyridazines. The results suggest that compounds containing one or two nitrogen atoms in the ring are suitable standards for correlating various heterocyclic compounds provided the nitrogen atoms are isolated from each other by carbon. Pyridazines do not appear to be evaluated correctly using pyridines and pyrazines as standards.

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Section: Resultscontrasting

confidence: 55%

Section: Resultsmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 78%

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An examination of the vaporization enthalpies and vapor pressures of pyrazine, pyrimidine, pyridazine, and 1,3,5-triazine

Lipkind

Chickos

2008

Struct Chem

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“…In view of this discrepancy and as semiempirical quantum methods are known to be unreliable for energy determinations, 47 we have preferred to use the group increment method proposed by Tjebbes 48 and by Vogel. 47 In this method, it is predicted that the substitution of a C-C bond by a C=C bond will have the same effect for the ther- …”

Section: Fig 5 Dative P(2 × 2)mentioning

confidence: 99%

Thermodynamic factors limiting the preservation of aromaticity of adsorbed organic compounds on Si(100): Example of the pyridine

Coustel

Carniato

Boureau

2011

The Journal of Chemical Physics

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Using pyridine as an example, a thermodynamic analysis of the low temperatures adsorption of aromatic organic molecules with a N atom on the Si(100) surface is presented. This study is restricted to the case of an equilibrium with the gas phase. Dative attachment which is the only way to preserve aromaticity is the more stable form of adsorbed pyridine in dilute solutions at low temperatures. Two factors limit the domain of stability of dative attachment: repulsive interactions between dative bonds prevent them from being present in concentrated solutions while aromaticity contributes to a decrease in the entropy, which explains the vanishing of dative bonds at high temperatures even in dilute solutions.

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“…These are segregated in Table 2 according to their dipole moments. The first group represents compounds characterized by dipole moments less than 3.0, 1,25−27 whereas the dipole moments in the second group exceed 3.0 D. 1,2,23,24 Two sets of experiments were conducted, duplicate runs with both sets of standards.…”

Section: Journal Of Chemical and Engineering Datamentioning

confidence: 99%

Vaporization, Sublimation Enthalpy, and Crystal Structures of Imidazo[1,2-a]pyrazine and Phthalazine

et al. 2015

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ABSTRACT:The vaporization enthalpy of imidazo [1,2-a]pyrazine is evaluated by correlation gas chromatography using two sets of standards and by transpiration. Vaporization enthalpies were evaluated using heterocyclic standards with dipole moments that vary from 0 to 3.0 D and using standards with dipole moments > 3.0 D. A value of (70.7 ± 1.0) kJ·mol −1 measured by transpiration compares to (67.9 ± 1.4) kJ·mol −1 measured by correlation gas chromatography using standards characterized by dipole moments > 3.0 D. The results suggest that imidazo[1,2-a]pyrazine is a member of this series of compounds whose vaporization enthalpies exceed those less polar heterocycles by a fairly constant amount, (6.9 ± 0.3) kJ·mol −1 , in this case by (5.9 ± 3.0) kJ·mol −1 using the less polar heterocycles. The crystal structures of phthalazine, another member of the polar series, and of imidazo[1,2-a]pyrazine were determined to examine whether π−π stacking, present in the solid state of two other members of the polar series, was a characteristic of this series. If present in the liquid, π−π stacking could offer a possible explanation for the vaporization enthalpy differences observed. The sublimation enthalpy of imidazo[1,2-a]pyrazine was also evaluated.

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The Heats of Combustion and Formation of the Three Diazines and their Resonance Energies.

Cited by 91 publications

References 0 publications

An examination of the vaporization enthalpies and vapor pressures of pyrazine, pyrimidine, pyridazine, and 1,3,5-triazine

An examination of the vaporization enthalpies and vapor pressures of pyrazine, pyrimidine, pyridazine, and 1,3,5-triazine

Thermodynamic factors limiting the preservation of aromaticity of adsorbed organic compounds on Si(100): Example of the pyridine

Vaporization, Sublimation Enthalpy, and Crystal Structures of Imidazo[1,2-a]pyrazine and Phthalazine

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