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

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.