A joint experimental and computational investigation on the thermochemistry of (nitrophenyl)pyrroles

Abstract

This paper reports the standard ( p° = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, Δ f H m ∘ ( g ) , at T = 298.15 K, of 1-(2-nitrophenyl)pyrrole and of 1-(4-nitrophenyl)pyrrole as (235.7 ± 2.7) kJ · mol −1 and (205.5 ± 2.5) kJ · mol −1, respectively. These values were derived from experimental thermodynamic parameters, namely from the standard ( p° = 0.1 MPa) molar enthalpies of formation, in the crystalline phase, Δ f H m ∘ ( cr ) , at T = 298.15 K, obtained from the standard molar enthalpies of combustion, Δ c H m ∘ , measured by static-bomb combustion calorimetry, and from the standard molar enthalpies of sublimation, at T = 298.15 K, determined from the temperature–vapour pressure dependence, obtained by the Knudsen mass loss effusion method. Additionally, the gas-phase enthalpies of formation were estimated by G3(MP2)//B3LYP calculations, using several gas-phase working reactions, and were compared with the experimental determined ones. Experimental and theoretical results are in very good agreement and show that 1-(4-nitrophenyl)pyrrole is thermodynamically more stable than the 2-isomer. This composite approach was also used to estimate the gas-phase enthalpy of formation of the 1-(3-nitrophenyl)pyrrole.