Experimental and theoretical study of methyl n-hydroxybenzoates

We determined the standard molar enthalpies of formation in gas-phase, at T = 298.15 K, of the methyl 2-, 3-, and 4-hydroxybenzoates, through static bomb combustion calorimetry and thermogravimetry. The enthalpies of formation in gas phase were derived from experimental combustion energies and phase-change enthalpies. In addition, we calculated the enthalpies of formation in the gas-phase with the Gaussian G4 composite method combined with atomization reactions and a Boltzmann weighted average to account for the conformational diversity of each compound. Experimental and theoretical determinations differ by less than 2 kJ·mol−1. We found that intramolecular hydrogen bonding strongly stabilizes methyl 2-hydroxybenzoate.