Thermochemical study of the methoxy- and dimethoxyphenol isomers

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

Authors

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

Journal

Title: Journal of Chemical & Engineering Data

Vol. 48

Pages: 669-679

ISSN: 0021-9568

Publisher: American Chemical Society

Indexing

ISI Web of Knowledge - 30 Citations

Scopus - 27 Citations

Scientific classification

FOS: Engineering and technology > Chemical engineering

Other information

Authenticus ID: P-000-GW0

DOI: 10.1021/je025641j

Abstract (EN): The standard (pdegrees = 0.1 MPa) molar enthalpies of formation for 2-, 3-, and 4-methoxyphenol and 2,3-, 2,6-, and 3,5-dimethoxyphenol in the gaseous phase were derived from the standard molar enthalpies of combustion, in oxygen, at 298.15 K, measured by static bomb combustion calorimetry, and the standard molar enthalpies of evaporation at 298.15 K, measured by Calvet microcalorimetry: 2-methoxyphenol, -(246.1 +/- 1.9) kJ mol(-1); 3-methoxyphenol, -(240.4 +/- 2.1) kJ mol(-1); 4-methoxyphenol, -(229.7 +/- 1.8) kJ mol(-1); 2,3-dimethoxyphenol, -(386.0 +/- 2.2) kJ mol(-1); 2,6-dimethoxyphenol, -(381.7 +/- 1.9) kJ mol(-1); 3,5-dimethoxyphenol, -(399.4 +/- 3.0) kJ mol(-1). Density functional theory calculations for all the methoxy- and dimethoxyphenols and respective phenoxyl radicals and phenoxide anions were performed using extended basis sets, which allowed the estimation of the gas-phase enthalpies of formation for all compounds. The good agreement of the calculated and experimental gas-phase enthalpies of formation for the closed-shell systems gives confidence to the estimates concerning the isomers which were not experimentally studied and to the estimates concerning the radicals and the anions. Substituent effects on the homolytic and heterolytic O-H bond dissociation energies have been analyzed, the results being in good agreement with available experimental data. Detailed analysis of these effects suggests that electronic exchange phenomena between the substituents dominate the effect the substituents have on these systems.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 11