Experimental and computational thermochemical study of three hydroxy-substituted phthalimides

We report experimental determinations of enthalpies and fusion temperatures, heat capacities (provided as polynomial functions of temperature), enthalpies of sublimation, and standard enthalpies of formation in the crystalline and gas phases at 298.15 K, for three phthalimide derivatives. These derivatives are N-hydroxy phthalimide, N-(hydroxymethyl) phthalimide, and N-(2-hydroxyethyl) phthalimide. The thermodynamic properties were experimentally obtained through thermal analysis techniques and combustion calorimetry. The enthalpies of formation in the gas phase at 298.15 K were calculated as well, using the G4 composite method in conjunction with atomization reactions and a Boltzmann weighted average that considers all stable conformers of each compound. The weights were estimated with the conformers' Gibbs energies. We found hydrogen bonds to be present in N-(hydroxymethyl) phthalimide and N-(2-hydroxyethyl) phthalimide, which were confirmed by means of theoretical analyses of the electron density. We also located weak non-covalent interactions in each stable conformer, which adds to the confirmation of hydrogen bonding. The experimental and theoretical thermochemical properties are in good agreement (less than 4 kJ difference per compound).