Journal of Chemical Thermodynamics, Vol.67, 190-196, 2013
Energetics and molecular structure of alkyl 1-methylpyrrolecarboxylates (alkyl = methyl or ethyl)
Calorimetric techniques, namely static bomb calorimetry and high temperature Calvet microcalorimetry were used to derive, respectively, the standard (p(o) = 0.1 MPa) molar enthalpy of formation, in the liquid phase, Delta H-f(m)o (l), and the standard molar enthalpy of vaporization, at T = 298.15 K, Delta H-g(l)m(o), of the methyl 1-methyl-2-pyrrolecarboxylate (M1M2PC). These experiments allowed the determination of its standard (p(o) = 0.1 MPa) molar enthalpy of formation, in the gaseous phase, Delta H-f(m)o (g) = -(270.3 +/- 2.2) kJ . mol(-1), at T = 298.15 K. Additionally, the standard molar enthalpy of formation of M1M2PC was estimated by computations based on standard ab initio molecular calculations at the G3(MP2)//B3LYP level. The estimated values are in very good agreement with experimental one, giving us support to estimate the gas-phase enthalpies of formation of the methyl 1-methyl-3-pyrrolecarboxylate (M1M3PC), ethyl 1-methyl-2-pyrrolecarboxylate (E1M2PC) and ethyl 1-methyl-3-pyrrolecarboxylate (E1M3PC), that were not studied experimentally. The molecular structures of the four molecules were established and the structural parameters were determined at the B3LYP/6-31G(d) level of theory. Furthermore, all the results were interpreted in terms of enthalpic increments. (C) 2013 Elsevier Ltd. All rights reserved.
Keywords:Enthalpy of combustion;Enthalpy of vaporization;Enthalpy of formation;Combustion calorimetry;High temperature Calvet microcalorimetry;G3(MP2)//B3LYP calculations;Methyl 1-methyl-2-pyrrolecarboxylate;Methyl 1-methyl-3-pyrrolecarboxylate;Ethyl 1-methyl-2-pyrrolecarboxylate;Ethyl 1-methyl-3-pyrrolecarboxylate