Thermochemical study of the ethylpyridine and ethylpyrazine isomers

• Type: Article in International Scientific Journal
• Date: 2003

Authors

Morais, VMF (Author) ICBAS; Miranda, MS (Author) Other; Matos, MAR (Author) FCUP

Journal

Title: Organic and Biomolecular Chemistry

Vol. 1

Pages: 4329-4334

ISSN: 1477-0520

Publisher: Royal Society of Chemistry

Indexing

ISI Web of Knowledge - 14 Citations

Scopus - 15 Citations

Scientific classification

FOS: Natural sciences > Chemical sciences

Other information

Authenticus ID: P-000-K8Y

DOI: 10.1039/b308097h

Abstract (EN): The standard (pdegrees = 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) U 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 6-31IG**. 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.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 6