Thermochemical study of 5-methyluracil, 6-methyluracil, and 5-nitrouracil

The standard (p° = 0.1 MPa) molar enthalpies of formation, in the crystalline phase, at T = 298.15 K, for 5-methyluracil, 6-methyluracil, and 5-nitrouracil were derived from the values of the standard massic energies of combustion measured by static bomb combustion calorimetry. The results obtained together with literature values of the enthalpies of sublimation yielded the standard molar enthalpies of formation, in gaseous phase, at T = 298.15 K. These values are discussed in the terms of structural enthalpic increments.

► Combustion calorimetry was used to determine ΔfHm∘(cr) of methyl and nitro derivatives of uracil.
► Gas phase ΔfHm∘ of methyl and nitro derivatives of uracil have been derived.
► The relative enthalpic stability of the title compounds is discussed in structural terms.