Thermochemistry of uracil and thymine revisited

• Thermochemistry of uracil and thymine was studied.
• Crystal state enthalpies of formation were measured by calorimetry.
• Sublimation enthalpies were derived by the transpiration method.
• Ab initio enthalpies of formation were in excellent agreement with experiment.

Thermochemical properties of uracil and thymine have been evaluated using additional experiments. Standard (p0 = 0.1 MPa) molar enthalpies of formation in the gas phase at T = 298.15 K for uracil −(298.1 ± 0.6) and for thymine −(337.6 ± 0.9) kJ · mol−1 have been derived from energies of combustion measured by static bomb combustion calorimetry and molar enthalpies of sublimation determined using the transpiration method. The G3 and G4 quantum-chemical methods were used for calculations of theoretical gaseous enthalpies of formation being in very good agreement with the re-measured experimental values.