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.