Experimental and computational energetic study of two halogenated 2-acetylpyrrole derivatives: 2-Trichloroacetylpyrrole and 2-trifluoroacetylpyrrole

The present work reports the values of the standard (p∘=0.1MPa) molar enthalpies of formation, in the crystalline phase, of 2-trichloroacetylpyrrole and 2-trifluoroacetylpyrrole, which were derived from the standard molar energies of combustion, in oxygen, to yield HCl·600H2O(l) and HF·10H2O(l), respectively, as well as CO2(g) and N2(g), at T = 298.15 K, measured by rotating bomb combustion calorimetry. The values of the standard molar enthalpies of sublimation, at T = 298.15 K, derived from the Knudsen mass-loss effusion technique are also presented. From the above mentioned experimental quantities, the standard molar enthalpies of formation, in the gaseous phase, were derived: ΔfHm∘(2-trichloroacetylpyrrole, g) = −(102.5 ± 1.6) kJ · mol−1 and ΔfHm∘(2-trifluoroacetylpyrrole, g) = −(704.7 ± 3.0) kJ · mol−1. These experimental values are compared with estimates based on high-level ab initio molecular orbital calculations at the G3(MP2)//B3LYP level, which have also been extended to the calculation of other thermodynamic properties namely N–H bond dissociation enthalpies, gas-phase acidities and basicities, proton affinities, and adiabatic ionization enthalpies.