Molecular energetics of pyrrolecarbonitriles and derivatives: A combined calorimetric and computational study

Highlights: ► Combustion calorimetry was used to determine ΔfHmo of the title compounds. ► Gas-phase ΔfHmo of the studied compounds have been derived by computational thermochemistry. ► Experimental and Computational values of ΔfHmo are in very good agreement. - Abstract: In this work, calorimetric measurements were carried out, in order to determine the standard (po = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, ΔfHmo(g), at T = 298.15 K, of 2-pyrrolecarbonitrile and 1,5-dimethyl-2-pyrrolecarbonitrile. These data were calculated from the standard molar enthalpies of formation, in the condensed phase, ΔfHmo(cr,l), at T = 298.15 K, derived from static bomb combustion calorimetry measurements, and from the standard molar enthalpies of phase transition, Δcr,lgHmo, at T = 298.15 K, obtained by high temperature Calvet microcalorimetry. The gas-phase enthalpies of formation were also calculated from high level ab initio molecular orbital calculations, at the G3(MP2)//B3LYP level, and a very good agreement between experimental and computational values was obtained, giving us support to estimate the gas-phase enthalpies of formation of 3-pyrrolecarbonitrile and 1,5-dimethyl-3-pyrrolecarbonitrile. Moreover, the molecular structure of the four molecules was established and the structural parameters were determined at the B3LYP/6-31G(d) level of theory.