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Thermochemical Study of Methyl n‑Methoxybenzoates: An Experimental and Computational Approach

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posted on 06.03.2019, 22:30 by Henoc Flores, J. Manuel Ledo, E. Adriana Camarillo, Juan M. Solano-Altamirano, Julio M. Hernández-Pérez, Fernando Ramos, Brenda Rabell
In this work, we determine, both experimentally and computationally, structural and thermochemical properties of the methyl 2- and 4-methoxybenzoates. Combustion and vaporization enthalpies of these compounds were obtained experimentally through combustion calorimetry and thermogravimetry. From these properties, their standard molar enthalpies of formation in the gas phase, at T = 298.15 K, were also determined. In addition, we computed gas-phase enthalpies of formation of methyl 2-, 3-, and 4-methoxybenzoates using the composite method Gaussian G4, atomization reactions, and a weighted Boltzmann average. This average was performed over the stable conformers of each compound, and the respective Gibbs energies were used to compute the weights for the Boltzmann average. The analyses of the electronic density of the molecules and of noncovalent interactions were performed as well. We found a good agreement between our experimental and computational enthalpies of formation of methyl 2- and 4-methoxybenzoates. Finally, we discuss the enthalpic effects, as a function of the relative position of the methoxy and methyl groups, upon the benzoate base structure.