Is Uracil Aromatic? The Enthalpies of Hydrogenation in the Gaseous and Crystalline Phases, and in Aqueous Solution, as Tools to Obtain an Answer

• Type: Article in International Scientific Journal
• Date: 2013

Authors

Tiago L P Galvao (Author) Other; Ines M Rocha (Author) Other; Maria D M C R Ribeiro da Silva (Author) FCUP; Manuel A V R Ribeiro da Silva (Author) Other

Journal

Title: Journal of Physical Chemistry A

Vol. 117

Pages: 5826-5836

ISSN: 1089-5639

Publisher: American Chemical Society

Indexing

ISI Web of Knowledge - 35 Citations

Scopus - 33 Citations

Scientific classification

FOS: Natural sciences > Chemical sciences

Other information

Authenticus ID: P-006-952

DOI: 10.1021/jp404938u

Abstract (EN): The enthalpy of hydrogenation of uracil was derived from the experimental enthalpies of formation, in the gaseous phase, of uracil and 5,6-dihydrouracil, in order to analyze its aromaticity. The enthalpy of formation of 5,6-dihydrouracil was obtained from combustion calorimetry, Knudsen effusion technique and Calvet microcalorimetry results. High-level computational methods were tested for the enthalpy of hydrogenation of uracil, but only with G3 was possible to obtain results in agreement with the experimental ones. It was found that uracil possesses 30.0% of aromatic character in the gaseous phase. Using both implicit, explicit, and hybrid solvation methods, it was possible to obtain a reference value for the enthalpy of hydrogenation of uracil in the aqueous solution and the effect of polarity and hydrogen bonds on the aromaticity of uracil was analyzed. The value of the hydrogenation enthalpy of uracil in aqueous solution was compared with the experimental value in the crystal phase, also dominated by polarity and hydrogen bonds, derived from combustion calorimetry results. The supramolecular effects on the crystal lattice were explored by the computational simulation of pi-pi staking dimers and hydrogen bonded dimers.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 11