Energetic characterization of uracil derivatives: Orotic and isoorotic acids

[Display omitted] •Experimental/computational energetic study of orotic and isoorotic acids.•Enthalpies of formation of the crystalline compounds from combustion calorimetry.•Enthalpies of sublimation of orotic and isoorotic acids were estimated.•Gas phase enthalpies of formation were estimated using the G3 and W1-F12 methods. The standard (po =0.1 MPa) molar enthalpies of formation of orotic and isoorotic acids, in the crystalline phase, were derived from the respective standard massic energies of combustion measured by static bomb combustion calorimetry, in oxygen, at T =298.15 K, as ‒821.7 ± 1.1 kJ mol−1 and ‒838.3 ± 1.9 kJ mol−1, respectively. The molecular structure and conformational behaviour of orotic and isoorotic acids were studied by theoretical calculations and the standard gas-phase molar enthalpies of formation were derived using an appropriate set of working reactions. Sublimation enthalpies, at the reference temperature T = 298.15 K, were estimated from difference between crystalline and gaseous enthalpies of formation and from statistically-based interaction indices derived from molecular surface electrostatic potentials.