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Issue 23, 2003
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Thermochemical study of the ethylpyridine and ethylpyrazine isomers

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Abstract

The standard (p° = 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.

Graphical abstract: Thermochemical study of the ethylpyridine and ethylpyrazine isomers

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Article information


Submitted
17 Jul 2003
Accepted
08 Oct 2003
First published
27 Oct 2003

Org. Biomol. Chem., 2003,1, 4329-4334
Article type
Paper

Thermochemical study of the ethylpyridine and ethylpyrazine isomers

V. M. F. Morais, M. S. Miranda and M. A. R. Matos, Org. Biomol. Chem., 2003, 1, 4329
DOI: 10.1039/B308097H

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