Enthalpies of combustion, heat capacities,and enthalpies of vaporisation of 1-phenylimidazole and 1-phenylpyrazole (original) (raw)
Related papers
Journal of Physical Chemistry B, 2011
The vaporization enthalpies of a series of heterocyclic compounds some suspected of showing evidence of a higher degree of self-association in comparison to many other nitrogen heterocycles have been measured both by correlation gas chromatography (CGC) and for comparison by transpiration. The compounds share some structural similarities. They include 2-and 4-(N,N-dimethylamino)pyridine, 1,5-diazabicyclo[4.3.0]non-5-ene, 1,8-diazabicyclo[5.4.0]undec-7ene, 1,2,4-triazolo[1,5-a]pyrimidine and imidazo[1,2-a]pyridine. The vaporization enthalpies of the first three of the compounds are well reproduced by a standard series of reference compounds, mainly pyridine derivatives. The latter two compounds and 4-(N,N-dimethylamino)pyridine exhibit vaporization enthalpies approximately 7 kJ 3 mol À1 larger. Their values are reproduced by using standards previously shown to exhibit stronger but similar self-association properties. The crystal structure of 1,2,4-triazolo[1,5-a]pyrimidine has been determined in an effort to understand the nature of the self-association. The molecule crystallizes in planar stacks slightly offset with a stacking distance of 3.24 Å.
The Journal of Physical Chemistry B, 2010
The vaporization enthalpies of 1-methyl-, 1-ethyl-, 1-phenyl-, and 1-benzylimidazole, 1-methyl-and 1-phenylpyrazole, and trans-azobenzene are evaluated by correlation-gas chromatography (C-GC) using a variety of azines and diazines as standards. The vaporization enthalpies obtained by C-GC when compared to literature values are approximately 14 kJ • mol-1 smaller for the imidazoles and 6 kJ • mol-1 smaller for the pyrazoles. The literature vaporization enthalpies of 1-methylpyrrole and 1-methylindole, two closely related compounds with one less nitrogen, are reproduced by C-GC. These results suggest that the magnitude of the intermolecular interactions present in 1-substituted imidazoles and pyrazoles are significantly larger than the those present in the reference compounds and greater than or equal in magnitude to the enhanced intermolecular interactions observed previously in aromatic 1,2-diazines. The vaporization enthalpy and vapor pressure of a trans-1,2-diazine, trans-azobenzene, measured by C-GC using similar standards reproduced the literature values within experimental error.
Journal of Chemical & Engineering Data, 2006
The vaporization enthalpies and vapor pressures of 1-, 6-, 7-, and 9-heptadecanol, 1-octadecanol, 1-eicosanol, 1-docosanol, 1-hexacosanol and cholesterol at T) 298.15 K have been measured by correlation gas chromatography using as standards, the even carbon n-alkanols from 1-decanol to 1-octadecanol and 1-pentadecanol. Fusion enthalpies for the all of these compounds were either measured by DSC or obtained from the literature. Adjusted to T) 298.15 K, the fusion and vaporization enthalpies were combined to provide sublimation enthalpies. The sublimation enthalpies were compared to existing literature values. Agreement between the two sets of values when available was generally very good.
The Journal of Chemical Thermodynamics, 2006
The standard (p = 0.1 MPa) molar enthalpies of combustion, D c H m , for the liquid compounds 1-methyl-2-piperidinemethanol, 1-piperidineethanol, and 2-piperidineethanol, were measured by static bomb calorimetry, in oxygen, at T = 298.15 K. The standard molar enthalpies of vaporization, at T = 298.15 K, of these three liquid compounds were determined by Calvet microcalorimetry.
Journal of Chemical & Engineering Data, 2006
The vaporization enthalpies and vapor pressures of 1-, 6-, 7-, and 9-heptadecanol, 1-octadecanol, 1-eicosanol, 1-docosanol, 1-hexacosanol and cholesterol at T) 298.15 K have been measured by correlation gas chromatography using as standards, the even carbon n-alkanols from 1-decanol to 1-octadecanol and 1-pentadecanol. Fusion enthalpies for the all of these compounds were either measured by DSC or obtained from the literature. Adjusted to T) 298.15 K, the fusion and vaporization enthalpies were combined to provide sublimation enthalpies. The sublimation enthalpies were compared to existing literature values. Agreement between the two sets of values when available was generally very good.
The Journal of Physical Chemistry B, 2011
The vaporization enthalpies of a series of heterocyclic compounds some suspected of showing evidence of a higher degree of self-association in comparison to many other nitrogen heterocycles have been measured both by correlation gas chromatography (CGC) and for comparison by transpiration. The compounds share some structural similarities. They include 2-and 4-(N,N-dimethylamino)pyridine, 1,5-diazabicyclo[4.3.0]non-5-ene, 1,8-diazabicyclo[5.4.0]undec-7ene, 1,2,4-triazolo[1,5-a]pyrimidine and imidazo[1,2-a]pyridine. The vaporization enthalpies of the first three of the compounds are well reproduced by a standard series of reference compounds, mainly pyridine derivatives. The latter two compounds and 4-(N,N-dimethylamino)pyridine exhibit vaporization enthalpies approximately 7 kJ 3 mol À1 larger. Their values are reproduced by using standards previously shown to exhibit stronger but similar self-association properties. The crystal structure of 1,2,4-triazolo[1,5-a]pyrimidine has been determined in an effort to understand the nature of the self-association. The molecule crystallizes in planar stacks slightly offset with a stacking distance of 3.24 Å.
Enthalpies of Formation of N -Substituted Pyrazoles and Imidazoles
The Journal of Physical Chemistry A, 1999
Accurate experimental enthalpies of formation measured using static bomb combustion calorimetry, the "vacuum sublimation" drop calorimetry method, and the Knudsen-effusion method are reported for the first time for four azoles: 1-methylimidazole (1MeIMI), 1-methylpyrazole (1MePYR), 1-benzylimidazole (1BnIMI), and 1-benzylpyrazole (1BnPYR). These values and those corresponding to imidazole (1HIMI), pyrazole (1HPYR), 1-ethylimidazole (1EtIMI), 1-ethylpyrazole (1EtPYR), 1-phenylimidazole (1PhIMI), and 1-phenylpyrazole (1PhPYR) are compared with theoretical values using the G2(MP2) and the B3LYP/ 6-311*G(3df,2p)//6-31G(d) approaches. In general, there is a very good agreement between calculated and experimental values for the series of N-substituted imidazoles, while the agreement is less good for the series of the N-substituted pyrazoles. Experimentally, the gap between the enthalpies of formation of imidazoles and pyrazoles decreases significantly upon N-substitution, while the theoretical estimates indicate that this decrease is smaller.
Thermal Study of Two Benzotriazole Derivatives
U.Porto Journal of Engineering
An experimental study based on the thermal analysis of 5-methyl-1H-benzotriazole and 5,6-dimethyl-1H-benzotriazole was developed, by using differential scanning calorimetry. Additionally, a summary of the experimental techniques and computational methodology being performed, in order to complement the energetic study of both compounds, is described. The knowledge of the thermochemical, thermophysical and structural properties of functionalized benzotriazoles is relevant for the evaluation of their chemical behaviour, as well as in the prediction of the reactivity of similar compounds that have not been thermodynamically characterized.
The Journal of Organic Chemistry, 1991
Enthalpies of vaporization of homologous series n-RY (Y = H, C1, Br, I, OH, SH, NH2, CN, COOH, OAc, and COOMe) or n-R1YR2-n (Y = 0, S, NH, CO) have been correlated with the respective carbon numbers or sums of carbon numbers. These correlations imply that enthalpies of vaporization of any two series are linearly related to each other. Other important implications of these correlations are (a) from the stand point of thermochemistry the fundamental unit of a normal alkyl is a methylene group and (b) the contribution to the enthalpy of vaporization of an alkyl group is transferable and additive. Enthalpies of vaporization of sequences of compounds with normal alkyls plot linearly against the respective enthalpies of formation. Branched alkyls are in all cases below the regression line. This is taken to be a thermochemical manifestation of the steric effect of branched alkyl groups. A set of steric substituent constants of branched alkyls from C3 to C5 has been derived from thermochemical data. Enthalpies of vaporization of sequences of compounds which belong to the same class, e.g. halides, are shown to be linearly related to the respective normal boiling points. A number of correlations between enthalpies of formation and normal boiling points are also reported. Trouton's ratios of homologous series of compounds n-RY or n-R1YR2-n are correlated with the respective carbon numbers or sums of carbon numbers. A method is proposed for estimating normal boiling points of high-boiling organic compounds with normal alkyl chains.