Thermal and structural properties of ethyl 2- and 3-aminobenzoates: Experimental and computational approaches

Abstract

Calorimetric experiments performed for ethyl 2-aminobenzoate and ethyl 3-aminobenzoate allowed the determination of their standard (p° = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, at T = 298.15 K. The techniques used were static bomb combustion calorimetry and high temperature Calvet microcalorimetry, which enabled the determination of the standard molar enthalpies of formation in the liquid phase, and the standard molar enthalpies of vaporization, at T = 298.15 K, of the above aminobenzoates.In addition, computational calculations, through the G4 composite method, were performed to estimate the enthalpies of formation in the gas phase of the title compounds. Boltzmann weighted averages were performed over sets of stable conformers of each compound, using Gibbs energy to compute population weights. The ethyl 2-aminobenzoate presents an intramolecular hydrogen bond, which was confirmed through topological analyses of the electron density.Furthermore, the energetic effect caused from exchanging the position of the amino substituent was evaluated, and was also compared with similar compounds.