Experimental and high level ab initio enthalpies of formation of di- tri- tetra- and pentamethyl- substituted pyrroles

• Experimental and computational thermochemical study of 1,2,5-trimethylpyrrole.
• ΔfHmo (g) derived from ΔfHmo (l) and ΔlgHmo.
• ΔfHmo(g) estimated for di-, tri-, tetra- and pentamethyl- pyrroles by G3(MP2)//B3LYP method.
• New value for the ΔfHmo of 2,5-dimethylfuran.

In this work, the 1,2,5-trimethylpyrrole was investigated by combining experimental (static bomb combustion calorimetry and high temperature Calvet microcalorimetry) and computational thermochemical (standard ab initio molecular calculations) results. The experimental value obtained for its standard (p° = 0.1 MPa) molar enthalpy of formation, in the gaseous phase, ΔfHmo(g) = (34.6 ± 2.6) kJ · mol−1, at T = 298.15 K, is in excellent agreement with the estimated data obtained at the G3(MP2)//B3LYP level using a set of gas-phase working reactions. Thereby, these calculations were further extended to estimate the gas-phase enthalpies of formation of all the di-, tri-, tetra- and pentamethylpyrrole derivatives, whose experimental value is not known.Moreover, a new value for the gas-phase molar enthalpy of formation of 2,5-dimethylfuran, as −120.2 kJ · mol−1, determined with the G3(MP2)//B3LYP composite approach, is suggested.